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Edited by 

Sven Anderson, M. E., 

/i 

Superintendent f loating Drydock Department, 
Maryland Steel Company. 


) 


> > 
> ) > 


> 


PUBLISHED BY 

THE MARYLAND STEEL COMPANY 

SPARROWS POINT, MX>. 

1907 . 



















































New Orleans Steel Floating Drydock. 

Starboard side wall heeled out of water for self-docking and for taking bolts out of under-water connections. 

































FLOATING DRYDOCKS—THEIR MILITARY POSSI¬ 
BILITIES AND VALUE.* 

By Rear Admiral John D. Ford, U. S. Navy. 


A modern drydock, like a battleship or ocean greyhound, is 
a development, and its successful construction requires extended 
study, careful design and good workmanship. In fact, it is an 
easier matter to construct a battleship than a dock, and no 
nation ought to be more appreciative of this fact than the 
United States. 

THE DEVELOPMENT OF THE DRYDOCK. 

In early days, when man’s weapons of war were spears and 
clubs, his war fleet probably consisted of canoes. Even these 
small boats had to be hauled on shore at times to be repaired 
or caulked with the simple stone or wooden tools of that age. 
After the canoe or dug-out had been dragged far enough upon 
the beach to permit repairs to be effected between the tides, 
the boat was again launched, and this constituted the genesis 
of the science that is now practiced of docking the largest of 
vessels. 

As man’s necessities increased or his desire to travel became 
more intense, the canoe developed into the galley, and the 
galley into the sailing ship. There were successive improve¬ 
ments which finally brought about the naval and merchant 
ships that now traverse the ocean. The sea craft of the suc¬ 
ceeding centuries thus became too unwieldy to be dragged on 
the sandy beach for repairs, and it became necessary to lay 
down inclined ways up which the vessel could be more readily 

* Reprinted by permission from Journal of the American Society of Naval 
Engineers, Volume XV, No. 1. 



6 


FLOATING DRYDOCKS. 


hauled from the water. T hen came the excavation with some 
crude form of gate or caisson for controlling both the egress 
and ingress of water to the dock. 

As there is an innate desire upon the part of man to have 
his works endure, it was not long before an attempt was made 
to strengthen the walls and base of the excavation, so that the 
basin or dock could not be destroyed by heavy rains, internal 
springs, or the natural tendency of the sides to cave in. 

It thus came about that the walls of the drvdock were con¬ 
structed of brick, wood, or granite, each material undoubtedly 
being the most suitable for special conditions and purposes. 

PARTICULAR CARE SHOULD BE EXERCISED IN LOCATING 

DRYDOCKS. 

It is because so many docks are not suitably located that they 
are a source of much trouble and expense. If it could be 
understood by those contemplating the construction of docks 
that it would be economy to give more study and reflection in 
locating these structures more docks would yield dividends, 
and their serious impairment would be of less frequent occur¬ 
rence. It is because some of the docks are constantly under 
repairs, due to being located in unsuitable places, that the cost 
of using them is so great. It can certainly be expected that the 
cost of maintaining the structures will be excessive unless the 
designers take into account the nature of the soil in which the 
excavation is made, the influence of the river currents, the an¬ 
nual downfall of rain in the vicinity, and many other factors 
of equal importance that must be considered in the determina¬ 
tion of location. 

It is often the case that all the factors that enter into the 
construction of a dock are not considered by those adminis¬ 
trators upon whom devolve the responsibility of deciding upon 
the location of the structure. The ability to enter and leave 
the dock with safety, the nature of the borings of the land 
in the vicinity, the proximity to manufacturing and terminal 
facilities, nearness to the sea, climate, and even geographical 


FLOATING DRYDOCKS. 


7 


reasons are elements that must be considered as having” an 
important influence in determining the future usefulness of 
the dock for military purposes. 

Unless the opinion of experienced experts is given more 
weight than that accorded individuals who have only casually 
taken up the question, it will be found that the expense of con¬ 
structing docks will be much greater than anticipated. It is 
because there is a lack of appreciation of the knowledge and 
experience required to design and construct a dock that we 
find that some of the structures are barely completed before 
the fact is evident that the dock is too short, too narrow, too 
shoal on the sill, or is insufficiently piled ; and thus, while pri¬ 
marily intended for large ships, it is only capable of being 
used by ships of medium size. 

A brief history of the docks now in course of construction 
at several naval stations ought to show conclusively that it 
would be wise policy to appoint a board of experts composed 
of men within and without the service whose sole duty it 
should be to investigate and report upon the character, location, 
size and number of docks necessary for naval purposes. 

THE FLOATING DRYDOCK. 

It would seem incredible that there should not be suitable 
places in every harbor of good size for the location of a per¬ 
manent drydock. From various causes, however, there are 
harbors where there are no suitable places, and, as a conse¬ 
quence, there has been invented the floating drydock, which 
can be built in convenient places and towed to the place where 
it is to be used. In fact, much more can be done with such a 
dock. The dock can be towed to the ship in distress, and, 
after the disabled vessel has been placed on the ways of the 
dock, the ship and dock could be towed to some sheltered har¬ 
bor, where repairs extending over months can be effected. The 
fact that floating docks are found in all parts of the world 
shows that it is not a great feat to tow such structures even 
thousands of miles. 


8 


FLOATING DRYDOCKS. 


VARIOUS COMPARTMENTS OF THE FLOATING DOCK CAN BE USED 

AS A REPAIR SHOP. 

Floating drydocks have been so improved that they have 
grown from the crude wooden affairs of the seventeenth cen¬ 
tury, mere wooden boxes with side walls and a pump, to the 
mammoth steel structures that will safely lift a battleship of 
15,000 tons. Further development can be expected, and 
therefore it ought to be apparent to the naval engineer and 
architect that the next advance should be in the direction of 
converting some of the side-wall compartments into work¬ 
shops, thus permitting many and even important repairs to be 
made with the mechanical resources of the dock. By thus 
utilizing the side compartments of the structure it will be 
possible, by towing such a dock near the base of operations, 
to keep the fighting ships much longer on the blockading line, 
since long trips to home ports might thus be avoided. 

One of the heavy expenses incurred in constructing and 
maintaining every form of dock is the expense of installation 
of machinery that is seldom used. While the vessel is in the 
dock, or the structure unused, the pumping power of course 
lies idle. As a matter of fact, the engines, pumps and boilers 
are used but a few days each month. By utilizing the pumping 
plants connected with the dock for the operation of work¬ 
shop tools, repairs could be cheapened as well as hastened. 
It is well within the range of probability that a ship entering 
such a dock might be supplied with light, cheap power and 
distilled water from the resources of the dock itself. In fact, 
such a structure might be regarded as a floating repair hulk 
as well as a floating dock. 

FLOATING DRYDOCKS A NECESSITY FOR EACH DISTANT NAVAL 

STATION. 

I 

With the great extent of coast line—Atlantic, Pacific, gulf 
and insular—that we must now defend, we should be possessed 
of at least four docks that could be towed and anchored in 
sheltered places in close touch with the probable scene of opera- 


FLOATING DRYDOCKS. 


9 


tion of our fleets. With such auxiliaries the hulls of our war 
vessels could be constantly kept clean, their higher speed main¬ 
tained, and repairs made that would lessen the tendency for the 
ships to leave their station in time of war or when important 
fleet maneuvers were being conducted. When our great extent 
of coast line is considered, it must be realized that we are very 
deficient in docking facilities in many localities where it is 
essential that we should possess such auxiliaries. 

As the scene of future naval operations upon the part of this 
country may be in some unexpected quarter, we should provide 
several floating docks, for their military value will be conclu¬ 
sively proved in the next naval war. 

THE COST OF A FLOATING DRYDOCK. 

The cost and management of a floating drydock is about 
one-half the cost of a graving dock when the latter is made in 
solid ground and under the most favorable conditions. The 
graving dock requires from three to six years to complete even 
under the most favorable conditions. It is necessarily located 
in a fixed place where it is subject to impairment from leaks 
and floods. With such a dock the damaged vessel, no matter 
how crippled her condition, must be taken to the docking struc¬ 
ture for repairs. 

In the case of the floating drydock the time of construction 
ought not to exceed from two to three years. Such a dock can 
be built anywhere, and even the several sections might be built 
at difference places, and thus the speed construction of the 
structure hastened in case of necessity. The appropriation 
available for the self-docking, steel, floating drydock for the 
Cavite naval station is $1,225,000. In reference to this dock it 
is stated: 

“It is the declared and acknowledged intention and meaning 
to provide and secure a complete and substantial self-docking, 
floating, steel drydock of American manufacture suitable for 
docking all of the present and projected ships of the United 
States Navy, for which appropriations have been made, located 


IO 


FLOATING DRYDOCKS. 


and installed in complete and perfect working order, together 
with all the moorings, wharves, approaches, accessories and 
appurtenances necessary for its perfect, complete and conve¬ 
nient operation and maintenance." 

The cost of a stone dock capable of doing this work would be 
certainly three to four times the appropriation that has been 
authorized for the construction of the self-docking steel struc¬ 
ture. 


CARE AND MANAGEMENT. 

Under competent management, floating drydocks can be 
moved about as safely as large hulks that are without motive 
power. The care and management of such docks is no more 
exacting than that required in operating large vessels where 
engineering experience and skill must be possessed. These 
docks have been towed in safety to all parts of the world. 
Where sections of the dock have been lost the cause can be 
traced either to terrible gales experienced, in which ships were 
also lost, or to carelessness upon the part of those in charge 
of the tow. 

SANITARY ADVANTAGES OF A FLOATING DRYDOCK. 

As the floating dock lifts the vessel above the surface of the 
water, the ship’s company and the workmen have better con¬ 
ditions as to light, air and atmospheric surroundings than they 
could secure in a vessel docked in the regular manner. The 
graving dock is damp and dingy, and it can not conduce to the 
health of the crew to inhale gases from the decomposition of 
the prass and scrapings from the ship’s side. 

There is no doubt but that the health of the men is seriously 
affected when a ship remains in a graving dock for some 
weeks, and the superiority of the floating dock is thus a matter 
of military importance. The fact should also not be forgotten 
that the graving docks are surrounded by machine shops in 
which there are hundreds if not thousands of workmen em¬ 
ployed, and that these artisans and laborers sometimes smuggle 


FLOATING DRYDOCKS. 


I I 

■spirituous liquor on board the ship in dock. Where it is only 
desired to clean and paint the vessel, a floating dock remote 
from such demoralizing influences would add greatly to the 
preservation of discipline and to the maintenance of good 
health. 

FLOATING DRYDOCK AT THE NAVAL STATION, NEW ORLEANS, LA. 

In view of the necessity of increasing the capabilities and of 
adding to the military value of our naval station on the Missis¬ 
sippi River, the Congress authorized the construction of a 
self-docking steel dock to be located opposite the City of New 
Orleans. The swift current of that river and the nature and 
character of the soil forbade the making of an excavation 
for a suitable graving dock. Military necessities thus com¬ 
pelled the construction of a floating type of dock for that sta¬ 
tion. It could hardly be expected that any endurance could be 
secured for a graving dock built on soil where it would be 
almost impossible to secure a proper foundation, and where the 
dock, after completion, might be seriously injured by the floods 
that are experienced in that vicinity. 

Another advantage of the floating dock at that point was 
its remoteness from the sea where there was no possibility 
of its being destroyed by an enemy. Its proximity to the city 
of New Orleans insures a supply of stores and material that 
may be requisite for efficient repairs. At this port there are 
also available thousands of skilled mechanics who can be 
employed in times of emergency. The shipping industry of 
that city is also of great extent, and thus in times of emer¬ 
gency men who have aptitude for sea life and who have had 
experience at sea might be recruited for the ships that were 
short in their complements. The proximity of this city to the 
coal fields of Alabama, and the cheapness with which coal 
can also be secured from Pennsylvania and Tennessee, make 
the port a desirable one for the establishment of a naval station. 

This floating dock was built by the Maryland Steel Com¬ 
pany, Sparrows Point, Maryland, in conformity with a circular 




FLOATING DRYDOCKS 



-TRANSVERSE SECT10N. 

.^5 Ordinary Floating Dock lifting Merchant Vessel. 



END E LEVATION. - 

Js Caisson Dock lifting Ironclad i 


HAVANA STEEL FLOATING DRYDOCK 













































































































































BOW OR UP 






xl 

tc 

l f) 



PLAN OP NEW ORLEANS STEEL FLOATING DRYJJOC'K. 


The connections for hinged bridges are shown on port side. 


The bilge blocks shown on plan were replaced by an improved system ot 
timber sills and docking keel blocks. 


Face p. 12—a 











































































































































































































































































































































































































































































































. 
























* 




































































































































































































































































> 



4 65-0 1 — 


The traveling cranes were omitted. 

The bracketed ends have no lifting power. 


SECTIONAL ELEVATION, NEW ORLEANS STEEL FLOATING DRYDOCK. 


Face p, 12—b 


The flying gangway is shown open. 

The pontoons were deepened two feet in excess of depth shown on plan. 


























































































































































































































































FLOATING DRYDOCKS. 


13 


issued to builders specifying the general character of a float¬ 
ing drydock for the U. S. Navy. 

The dock was built from English plans and specifications that 
had been revised and modified by the Bureau of Yards and 
Docks, Navy Department. Before the contract was signed, 
particular attention was given to improvement in detail. 

THE CONTRACT FOR THE DOCK. 

The contract was signed April 10, 1899, the price being 
$810,000. The time allowed for completion was eighteen 
months, which time was afterwards extended to May 26, 1902. 
The principal causes for the delay were the difficulty experi¬ 
enced in procuring material and the inability of the mechanics 
at Sparrows Point to continue work in rainy and severe weather 
upon a structure where shelter could not be secured. 

The contract required that the dock should be built of mild 
steel of American manufacture, and of the best workmanship, 
all material and work to be inspected by an officer representing 
the Navy Department. 

The contract required that the structure should be secured 
with two steel bridge booms connecting the dock with the 
shore by means of steel piers—one boom fixed near its bow 
and one secured to the stern. The booms are to be hinged 
both at the dock and at the pier ends so as to accommodate 
themselves to the sinking and raising of the dock. 

The dock was to be capable of raising a ship of 15,000 tons 
to a height of six feet above the surface of the water, or sus¬ 
taining a vessel of 18,000 tons with the deck of the dock awash. 
There was also required that the 15,000-ton vessel should be 
raised within 3^ hours from the time of entering the dock. 
This period was to include the time for mooring the ship, 
pumping out the dock and making all the lifting operations 
necessary for the proper securing of the ship. The dock was 
also to be supplied with winches, bollards, etc., and to be capable 
of docking any of its own pontoons. 



i4 


FLOATING DRYDOCKS. 


CONSTRUCTION OF THE DOCK. 


Immediately after the contract was signed, Civil Engineer A. 
C. Cunningham, U. S. N., was detailed by the Department to 
superintend the construction. This officer remained on duty 
until the dock was officially accepted. Under his general direc¬ 
tion detailed drawings were made, material ordered, exca¬ 
vations completed and the dock secured in place. The work 
on the dock was greatly facilitated by the use of gang punching 
machines, which spaced and punched the holes as evenly and 
equally as if templates had been used. The dock was floated 
October 5, 1901. Ten days later it left Sparrows Point in 
tow, and arrived at New Orleans, La., November 6th, with¬ 
out mishap. 

GENERAL DIMENSIONS OF THE DOCK. 


Length over all, feet. 

Breadth over all, feet arid inches. 

between fenders on walls, feet. 

Maximum draught, feet. 

Depth over sills, feet. 

Length of walls, feet and inches. 

Width of walls, feet and inches. 

Freeboard of walls, feet. 

sills, feet and inches. 

Number of pontoons. 

Length of middle pontoon, feet. 

end pontoon, feet and inches. 

Depth of pontoons, feet and inches. 

Clearance between walls and pontoons, feet. 

Number of watertight compartments in middle pontoon. 

each end pontoon. 

supporting bulkheads in middle, fore and aft. 

frames. 

bulkheads, athwartship. 

each end pontoon, fore and aft. 

athwartship 


frames, fore and aft. 

Distance from center to center of frames, fore and aft, ft. and ins... 

Outside plating, thickness, inch. 

Distance from center to center of rivets. 

Diameter of rivets. 

Number of keel blocks... 

Height of keel blocks, feet.. 

Weight of dock, tons. 


525 

I26—2yV 
IOO 

50 

28 

395-of 

12-14 

28 

4-9 

3 

240 

141-04 

17-6 

2 

16 

8 

3 

26 

5 

3 
5 
9 

2-6 

°f 

Varies. 

Varies. 

209 

4 

6,122 




























floating drydocks. 


15 


THE PUMPING MACHINERY. 

The pumping machinery is installed in the side-wall com¬ 
partments. At the bottom of each wall are placed four cen¬ 
trifugal pumps which discharge directly outboard. The pumps 
are horizontal, with branch pipes leading through all the water¬ 
tight compartments of the side walls and pontoons. Each 
pair of pumps is driven by a vertical, compound, non-condens- 
ing engine, which is installed in the central and upper compart¬ 
ments of each side wall. 

Steam is furnished by four Babcock and Wilcox water-tube 
boilers, one boiler being provided for each engine. The steam 
piping is so arranged that any engine can take steam from any 
boiler. Each boiler, engine and pump is of standard size, thus 
making it possible to have an interchangeability of parts in case 
of breakdowns. The main pumps are connected by vertical 
shafting and gearing to their respective engines. The engines 
are fitted with automatic flywheel governors, which are in¬ 
tended to maintain a regular speed of 300 revolutions per 
minute, no matter what the fluctuations of the water load 
may be. 

DIMENSIONS OF MACHINERY. 

The following are the principal dimensions of the compound, 
vertical pumping engines: 


Number of engines. 4 

H.P. cylinder, diameter, inches. 13 

L.P. cylinder, diameter, inches. 22 

Stroke, inches. 12 

Main shaft, diameter, inches. 4f 

Vertical shaft, diameter, inches. 3^ 

Gearwheel, diameter, inches. 16 

Pumps, main, number. 8 

Pumps, horizontal centrifugal. 8 

Suction pipe, diameter, inches. 16 

Discharge pipe, diameter, inches. 16 

Revolutions, maximum. 410 

minimum. 310 

Capacity of each pump, gallons per minute. 5,000 

all pumps, gallons per minnte... 40,000 

Drains : Diameter of main drain, inches. 18 

2d branches, inches. 12 

3d branches, inches. 8 




















i6 


FLOATING DRY DOCKS. 


GENERAL DESCRIPTION OF BOILERS. 

Steam is furnished bv four Babcock and Wilcox cross-drum 

j 

boilers. The casings are of steel lined with asbestos. 


Number of boilers. 4 

tubes in each boiler. 90 

Length of tubes, feet. 14 

Diameter of tubes, inches. 4 

Grate surface, each boiler, square feet.. 33i 

Total grate surface, square feet. I33i 

Heating surface, each boiler, square feet. 1,356 

all boilers, square feet. . 5,424 

Hydrostatic pressure to which boilers were subjected, pounds. 225 

Working pressure of boilers, pounds. 160 


Worthington pumps are installed in each wall compartment 
for washing down and fire service. 

OPERATION OF THE DOCK. 

The whole dock is operated from a central station house on 
each side wall. In these stations levers are placed by means of 
which the v^lVes are operated. Signals are arranged by means 
of which the position of every valve can be known at a glance. 
Each station is in direct communication with those in charge 
of the engine and firerooms by means of speaking tubes, and 
thus the dockmaster has complete control of every pump and 
valve. The docking of the ship can thus be manipulated with¬ 
out the dockmaster leaving his central station. The dock is 
moored by four stud-link chain cables, to each of which are 
attached mushroom anchors. These anchors are handled by 
capstans connected to winches which are installed on the upper 
deck of the side walls. The dock is also connected to shore 
steel columns by two steel lattice booms, which are free to 
move in all directions to accommodate for the rise and fall 
in the river, which is subject to great fluctuations. These 
connections also permit the dock to be swung in toward the 
shore so that the structure need not be exposed to the strongest 
current of the river. 

The side walls are provided with flying gangways, which 












FLOATING DRYDOCKS. 


17 


are placed at the bow end of the dock, hinged so as to swing 
together. 1 he side walls are fitted with platform and protect¬ 
ing hand rails to provide a means of passing from one section 
to the other. Convenient ladders and stairways are placed on 
the inside of the side walls to reach the upper decks from the 
pontoon deck. Light swinging hand cranes are provided on 
each gangway deck for handling material. There are also 
provided fair-leads and other appliances for handling the 
necessary lines required for docking the vessels. 

IMPROVEMENTS IN THE ORIGINAL DESIGN OF THE NEW 

ORLEANS DOCK. 

A general plan of the New Orleans dock accompanies this 
paper from which its general design and arrangement can be 
seen. A general plan of the Havana floating dock, which is of 
the same general design, is also given. From a comparison of 
the two docks it will be seen that there are numerous improve¬ 
ments in the New Orleans dock, the principal one being the re¬ 
duction in number of pontoons from five to three. Using 
fewer pontoons of greater length tends to produce a dock of 
much greater longitudinal stiffness by reducing the number 
of junctions in pontoons. Such a design also makes a more 
continuous structure, and thus there is a stiffening of the 
center pontoon, where the heaviest weight must be carried. 
The most important improvement made in the English design 
of the New Orleans dock was the deepening of the pontoons 
by two feet and the stiffening of their decks, so that blocking 
could be placed at any point. These requirements, besides giv¬ 
ing greater freeboard to the deck of the dock and making 
it much stronger for working purposes, added greatly to its 
longitudinal stiffness, and without them it is doubtful if it 
would have passed a satisfactory test under the load of the 
Illinois. 

The new floating dock for the British Government at Ber¬ 
muda was designed at the same time as the New Orleans dock 
and by the same English firm of designers. Had it not been 


2 


i8 


FLOATING DRYDOCKS. 


HAVANA FLOATING DOCK. 

■-Stability Curves.- 




F.j X. 


Tig. \ 


(7TO 




n 






.mrr. 



r>* 2 


’»>! * 


End View of Self-Docking Operation. 


for the Bureau of Yards and Docks requiring the deepening 
of the pontoons by two feet, the Bermuda dock would have 
exceeded the New Orleans dock in lifting capacity by several 
hundred tons. 

DESIRABLE IMPROVEMENTS. 

The New Orleans floating drydock has the greatest lifting 
capacity of any dock of its type. In workmanship, equip¬ 
ment and machinery, as well as in facility of operation, it is 
considered superior to any floating dock yet built. There are. 











































A K 1 blocks. 

B Slicing bilge blocks. 

C M hanical self-centering side shores 


0 Spring roller fendei 1 
E Spring rubbing timber 


F Gangway passages 
G Caissons. 


H Grooves for caissons. 

J Flying gangway and crane 


K Hand cranes. M Ladders. 

L Mooring bollards and cables. N Valve house 



450 . o '/2 

SIDE ELEVATION. 


Mess?C.S. Swan & Hunter l!Wallsend .Contractors 



Lifting capacity, 10,000 tons 


For battleships, the space 


HAVANA STEEL FLOATING DRYDOCK. tt i ^ * u 

Towed from England to Havana. 

After being broken in two, between the second and center pontoons in self docking, each section was separately towed to Pensacola. 

enclosed by the altars and decks of pontoons is made watertight by placing shallow caissons at the ends, and strips over the junctions of 


pontoons, thus forming a shallow graving 


dock. This feature was eliminated from the New Orleans dock by the Government. 


Face p 18. 












































































































































































































































































































































































































1 


, 

;J9 

. 


' 




























4 


’ 

















I 














FLOATING DRYDOCKS. 


19 


however, some featiues about this dock where improvements 
could be made. Some of the objections are inherent to the 
type, and a few are not. For instance, the ends of the dock 
are made pointed, and the side walls are shorter than the 
dock and stepped back on the ends. W hile this construction 
lends to economy of material, it prevents the docking- of a 
ship in the end of the dock, and tends to heavy strains in the 
side w r alls, if the unloaded end compartments of the pontoons 
are unduly pumped from. 

The lower self-docking- connections on this dock are always 
under waiter, unless the dock is specially heeled to bring them 
out. While this is not a serious matter in the fresh water at 
New' Orleans, it becomes a vital objection in salt water, since 
even a little neglect will cause these joints to rust to an extent 
that self-docking might become a difficult matter. The side 
walls are self-docked by being canted out of water, and, as 
the inner edges are only raised about two feet clear, the space 
is not as great as it should be for convenient repairs. 

TESTING THE DOCK. 

After the arrival of the dock at New Orleans a special 
board, of which the writer was a member, composed of offi¬ 
cers of the Navy, w r as detailed by the Honorable Secretary of 
the Navy for the purpose of examining and testing the dock. 
It was found to be impossible to maintain the proper depth 
of w r ater at the site originally selected for the location of the 
dock, due to the shifting nature of the bottom of the river. 
The mechanical feature of the test was a complete success. 
During this official test the dock wtis lowered and raised several 
times, in order to test every feature of the structure. It was 
thus also possible to note the aptitude and ability of the people 
intrusted wdth its handling. It was soon demonstrated that 
there w r as not a sufficient depth of water to enable the dock 
to be lowered to its greatest w'orking depth. Divers were sent 
down to examine the bottom. Wreckers were employed to 
remove the obstructions, and then it was found that the hind- 


20 


FLOATING DRYDOCKS. 


ranee consisted of sunken and broken coal barges, lighters and 
other abandoned wreckage that had probably accumulated 
there from the time of the civil war. Around about the several 
wrecks there had accumulated considerable silt, thus reduc¬ 
ing the depth of the water at the appointed site. In all the 
tests the dock performed satisfactorily. The crew in charge 
also demonstrated their ability to operate efficiently every aux¬ 
iliary connected with the structure. 

On December 30, 1901, the U. S. Navy collier Sterling was 
placed in the dock, and the vessel raised until the dock had 
two feet six inches freeboard. It was done in two hours. As 
the docking of the Sterling was merely a preliminary test, no 
attempt was made to expedite the work, and yet it was done 
in two hours. The bottom of the Sterling was cleaned and 
painted while the vessel was in dock, after which the structure 
was lowered and the collier steamed out to her anchorage in 
the river. The following are the general dimensions of the col¬ 
lier Sterling : 


Length over all, feet. 275 

Breadth of beam, feet. 37 

Draught, feet and inches. 22-S 

Displacement, tons. 5,663 


DOCKING THE BATTLESHIP "ILLINOIS." 

After the collier was undocked further efforts were made by 
the contractors to secure a greater depth of water under the 
structure at the site selected. As all such efforts were un¬ 
availing, the attempt was abandoned. On January 4 and 5 the 
top row of keel blocks was removed, and arrangements were 
made for docking the battleship Illinois. 

At 10.30 A. M. on January 6, 1902, the Illinois , with her 
crew, armament and stores on board steamed up to the en¬ 
trance of the dock, and two hours later she was placed within 
the structure. In exactly two hours she was raised to the 
amount required, which was forty minutes less time than 
allowed by the contract. The following are the general di¬ 
mensions of the Illinois: 







Docking the Battleship “Illinois” in the Floating Drydock at the U. S. Naval Station, 

New Orleans, La., January, 1902. 




















Self-Docking the Middle Pontoon of the Floating Drydock at the U. S. Naval Station, 

New Orleans, La. 






























FLOATING DRYDOCKS. 


21 


Length over all, feet. 

Beam, feet and inches.. 

Mean draught, feet and inches 
Displacement, tons. 

The Illinois remained in dock three days. She was un¬ 
docked in less than three hours, after which the dock was 
carefully examined by the various members of the special board 
appointed to observe its working. No defects were discovered, 
and arrangements were then made to self-dock the various 
pontoons. This was also successfully accomplished. The dock 
was preliminarily accepted May 22, 1902. 

EASY BEARING OF A VESSEL ON A FLOATING DOCK. 

An interesting fact connected with the docking of the Illinois 
was the discovery that the cement in her double bottoms was 
not cracked when the ship was lifted, thus showing that the 
vessel was carried very easily and without strain. It was also 
found that the keel blocks were neither marked nor dented, 
although the battleship was carried on the deck for over three 
days. The only thing found on the keel blocks was the paint 
that came from the bottom of the ship in contact with the 
blocks. It is thus of importance to note that there was neither 
cracking of the cement nor cutting of the blocks, proving that 
the tender bottom of a battleship can be carried on a well-de¬ 
signed floating dock with an evenly distributed pressure and 
without a tendency to strain. 

SCOURING UNDER THE DOCK. 

Preceding the docking of the Illinois great efforts were made 
by the contractor to dredge the located site to the necessary 
depth, so that the structure might be sunk to the full depth 
to which it was designed to be lowered. Although all wreck¬ 
age had apparently been cleared away, the dredging seemed 
of no avail, as the site filled up as fast as material was re¬ 
moved. 

Since the docking of the Illinois , a natural scour has set in 
under the dock, and the continuous flow of water under the 


369 

72-2^ 

24-I-J 

11,565 






22 


FLOATING DRYDOCKS. 


structure has carried away all of the soft material, leaving a 
splendid foundation of clay at even a greater depth than is 
necessary for the extreme sinking of the dock even at the 
lowest stages of the river. Several months* observation indi¬ 
cate that the scouring under the dock is permanent, and that 
no future trouble may be anticipated from lack of required 
depth for sinking the dock sufficient to enter any battleship 
that we possess. 

DRIFT AND WRECKAGE. 

Some difficulty was anticipated from floating and submerged 
wreckage, and yet but little trouble has been experienced in 
this direction. The greater part of the drifting material passes 
well clear of the structure by reason of the fact that the set 
of the current is on the side of the river opposite the dock. 
From time to time a diver, who forms part of the dry- 
dock’s crew, makes an examination under the dock, so that 
assurance can be had that the dock is capable of being lowered 
to its maximum depth at early notice. 

WORKSHOPS AND DOCKS ESSENTIAL TO THE EFFICIENCY OF 

EACH OTHER. 

No other Government ship has been docked at New Orleans 
since the Illinois was at the station. The fact that the naval 
station at New Orleans does not contain well-appointed shops 
where extensive repairs can be effected has probably influenced 
the Department to some extent in not docking other battle¬ 
ships at that point. This condition emphasizes the important 
point that in the establishment of a naval station the progress 
of development should be so carried on that both docking 
facilities and workshops should be completed about the same 
time. 

NAVAL DRYDOCKS ARE NECESSARY AUXILIARIES TO THE DEVEL¬ 
OPMENT OF OUR MERCHANT MARINE. 

While the Illinois has been the only warship that has been 
docked at our naval station on the Mississippi, the structure 
has been extensively used by merchant shipping, and has 


FLOATING DRYDOCKS. 


23 


proved a great boom to the maritime interests of the gulf. 
The small local floating docks at New Orleans are very old. 
None have a capacity exceeding 1,200 tons, so that there were 
practically no docking facilities at that port for ocean-going 
vessels before the arrival of the Navy floating dock. Since 
the maritime interests have been assured that docking can be 
successfully accomplished at the New Orleans station, the 
larger class of merchant vessels no longer hesitate to visit the 
port, since they now fully realize that in case of necessity the 
hulls can be readily cleaned and the most important repairs 
effected with the aid of the machine shops at New Orleans. 

Standard rates for docking merchant ships have been estab¬ 
lished by authority of the Navy Department. By permitting 
the merchant marine to use the dock our coastwise trade is 
benefited. The efficiency of the dock is also maintained. It 
is non-use of every structure which brings about deterioration, 
and thus the Department is subserving national and commercial 
interests by using the dock as much as possible. Up to the 
present time the revenue received from docking fees has paid 
the current expense of the station, and has even provided a 
fair rate of interest on the original investment. 

A FLOATING DOCK FOR THE PHILIPFINES. 

The successful and satisfactory docking of the battleship 
Illinois in the New Orleans self-docking structure has led the 
Congress to make an appropriation for another large floating 
drydock for the Philippine Islands. The Navy Department 
has recently issued a general specification for this dock. It is 
to be hoped that a number of firms will be induced to bid for 
the construction of this dock so that general interest through¬ 
out the country can be manifested in this work, and thus the 
thought and energy of many be directed to making progressive 
improvements. 

In the preparation of the specifications advantage has been 
taken of the information secured from New Orleans. Careful 
consideration has also been given to overcoming the defects 


24 


FLOATING DRYDOCKS. 


experienced in other floating docks. The unfortunate accident 
bv which the Havana dock was broken in two has likewise been 
the means of calling attention to certain inherent weaknesses 
that must be carefully considered. In greatly improving the 
efficiency, usefulness and endurance of the new dock for the 
Philippines, the accident to the Havana structure has not been 
altogether a serious loss. 

The following are the principal dimensions of the dock for 
the Cavite naval station: 


Length overall, feet. 5 °° 

Width between fenders, feet. ioo 

Height of side walls clear above the water, feet. 

Draught over four-feet keel blocks, feet. 30 

Lifting capacity, tons. 16,000 


The dock will be able actually to lift above the water, with 
the pontoon decks awash, 20,000 tons. The limited strains on 
material and the requirements for pumping are such that only 
gross carelessness or inefficiency can disable the dock. All self¬ 
docking connections will be installed above water, where they 
will not be liable to deterioration. For self-docking purposes, 
all under-water portions will be required to be raised at least 
five feet out of water. It is believed that a full compliance 
with the official requirements of the Navy Department will 
cause the floating dock for the Philippines to stand as the 
future type for the Navy. 

The dock proper is to be entirely completed and ready for 
test in every respect within twenty-seven months from date of 
contract. 


THE MILITARY IMPORTANCE OF SUCH DOCKS. 

Floating drydocks are certain to play an important part in • 
future naval operations. The ease and rapidity with which 
they can be built, the ability to transfer them from port to 
port, and their adaptability to localities where graving docks 
cannot be constructed gives them an importance that can be 
no longer disregarded. Under existing conditions the dock 








FLOATING DRYDOCKS. 


25 


question is of vital importance for keeping the fighting ships 
in a high state of efficiency. The problem of the dock, and 
particularly the possibilities of the self-docking drydock, is one 
that is worthy of the closest study of our naval strategists and 
administrators. 

Editor’s Note.— The New Orleans dock was installed at 
the New Orleans Naval Station by the contractors. It was 
insured in passage and towed by the Boston Tow Boat Co. 
No elaborate preparations were made for towing. The pointed 
and sloping ends of the dock were planked over to form a 
bow and stern ; but as the dock was seldom if ever in line with 
the tow on the passage, this expedient proved of no value. 
A bridle was formed of one of the mooring chains, and to this 
was attached two sea-going tugs in tandem, the one nearest 
the dock being fitted with a towing machine. Although some 
heavy weather was encountered on the trip nothing of especial 
moment happened. 



2 6 


FLOATING DRYDOCKS. 




THE CAVITE STEEL FLOATING DRYDOCK.* 

THE STRATEGIC VALUE IN DEFENDING THE PHILIPPINES. 
By Civil Engineer A. C. Cunningham, U. S. Navy. 


The Congress of the United States, in the act making - pro¬ 
vision for the support of the naval service, which was approved 
July i, 1902, authorized the expenditure of $1,225,000 for a 
steel floating drydock for the Cavite Naval Station. The act 
provided that the material of the dock should be of American 
manufacture, and that it should be constructed under the direc¬ 
tion of the Bureau of Yards and Docks, Navy Department. 

CONGRESSIONAL APPRECIATION. 

Thoughtful consideration will show the wisdom of this 
action, and the quick appreciation of the military situation in 
the Philippines. A few months before the naval appropria¬ 
tion bill was enacted into law, the New Orleans floating dry- 
dock had been accepted, after it had demonstrated the capa¬ 
bility of a well-constructed floating steel structure to dock 
safely a modern first-class battleship. The docking of the 
battleship Illinois in this structure had been accomplished under 
disadvantages and unusual conditions, and the test conclusively 
showed that such a design of dock possessed a distinct military 
value. The test also demonstrated that, owing to its properly 
limited elastic qualities, such a dock will carry a first-class 
battleship more easily and uniformly than the land or graving 
structure. 

The behavior of and conditions surrounding the New Or¬ 
leans floating structure in docking the Illinois had been par¬ 
ticularly inquired into by the House Naval Committee, in con- 

* Reprinted by permission from Journal of the American Society of Naval 
Engineers, Volume XV, No. 2. 







FLOATING DRYDOCKS. 


2 7 


nection \\ ith the question of the establishment of a graving 
dock for an extensive naval station in the Philippines. 

The Spanish authorities had left unsolved the problem of 
selecting a suitable site for a permanent naval station. The 
Congress was somewhat reluctant to authorize heavv expendi¬ 
tures for a naval establishment that would ultimately have to 
be defended by extensive land fortifications, and it was there¬ 
fore believed that the nation's interest would best be secured 
by the construction of a floating steel structure which could be 
first used at Cavite, and then transferred to another point if 
necessary. 

The problem of selecting a site for the most important naval 
station in the far east was regarded by the Congress as a very 
serious one. It was believed that reasons of national policy 
demanded that the question be postponed for a few years. 
The problem actually involved topographical, industrial, 
strategical and political considerations which were not easily 
reconciled. It was, therefore, undoubtedly a wise policy which 
prompted Congress to authorize the building of a floating dock 
at Cavite for temporary, if not for permanent, purposes. 

OUR PAST EXPERIENCE WITH GRAVING DOCKS. 

While the question of authorizing the building of an exten¬ 
sive naval station in the Philippines was under consideration 
the Navy Department was experiencing considerable trouble 
in regard to the graving docks that had been in course of con¬ 
struction at several naval stations on the Atlantic coast. Not 
only were some of the contractors backward in the work, but 
it seemed essential at certain stations to cancel existing con¬ 
tracts. In the building of these structures some of the con¬ 
tractors had apparently forgotten to take into consideration 
the character of the soil in which the docks were to be built, 
the facilities for securing supplies and labor, the nature of the 
prevailing tides, winds and currents, and the danger from 
flooding. While the Department had taken special means to 
inform the several bidders as to the necessity of taking into 


28 


FLOATING DRYDOCKS. 


consideration each and all of these factors, some of the suc¬ 
cessful bidders apparently had failed to consider all of the im¬ 
portant features. 

The delay in building - the graving docks at the several navy 
yards, contrasted with the rapid delivery of the New Orleans 
steel floating dock, was undoubtedly an important considera¬ 
tion in securing the authorization for the Cavite structure. 
Our experience in building cement docks had conclusively 
shown that such structures could not be built in less than six 
years, while the floating dock could be constructed in just 
half that time. In the case of the cement or stone docks the 
cost in every case will practically exceed the estimates to a 
considerable amount, not taking into consideration the loss 
from delay. The floating structures were built at contract 
price. The New Orleans dock had also shown that the struc¬ 
ture itself might contain repair facilities of considerable extent. 

The floating dock also commended itself to the consideration 
of many members of the House Naval Committee by reason 
ot die fact that the element of time in construction was in favor 
of the floating structure. Then, again, the dock could be 
towed to the shops, and in the case of the Philippines the shops 
might be a fleet of warships, while in the case of the graving 
dock a series of shops would have to be built. When a ship 
can be taken from the water it is a very unusual casualty which 
her own crew and equipment can not at least make temporarily 
good, providing labor and material can be brought to the 
vessel in the dock. In the Philippines we have all manner 
of auxiliaries to the fighting ship, and if one of the battle¬ 
ships should reach the floating dock the auxiliary vessels could 
render much service, in bringing, where necessary, men and 
material from China and Japan. 

The problem of commencing the building of a great naval 
station in the Philippines was therefore happily solved by 
authorizing the construction of a floating dock. This action 
will give the commander-in-chief of the Asiatic Station a dock 
that will safely carry any battleship under his command. The 
dock will also be available for use at least two years sooner 


FLOATING DRYDOCKS. 


2 9 


than any stone or cement dock could be built. It will not only 
be serviceable for use at Cavite, but for any point in the Phil¬ 
ippines which may be ultimately selected as the site for the 
naval station. The Navy Department will thus have more 
time to investigate the possibilities of other points than those 
already surveyed as a proper site for our central naval station. 
Altogether, a wise decision was reached when the construction 
of the floating dock for Cavite was authorized. 

PRELIMINARY CONDITIONS. 

The appropriation having been made, it lay with the Bureau 
of Yards and Docks to execute the project. That Bureau had 
just completed the best floating dry dock in existence, and a less 
progressive naval establishment would have been satisfied to 
duplicate this dock. The Bureau, however, had given con¬ 
tinuous study to the floating-dock problem during the con¬ 
struction of the New Orleans dock, and had taken careful note 
of all developments and happenings in this line. 

It was found that although much more had been secured in 
this dock than had heretofore satisfied most nations, there 
w r ere still many features desirable in the matter of strength, 
convenience and equipment in a floating-dock structure fully 
to meet the needs of an exacting and progressive naval service. 

It was therefore determined to make a general specification 
covering all the desirable conditions, and to allow the compe¬ 
tition of the world’s experts in producing a design which 
should most fully meet the needs of the naval service. 

THE SPECIFICATION. 

The leading requirements of the specification are here given. 

Paragraph 1. Intention .—“It is the declared and acknowl¬ 
edged intention and meaning to provide and secure a com¬ 
plete and substantial self-docking floating steel drydock of 
American manufacture, suitable for docking all the present 
and projected slnps of the United States Navy, for which 
appropriations have been made, located and installed in perfect 
working order, together with all moorings., wharves, ap- 



30 


FLOATING DRYDOCKS 


proaches, accessories and appurtenances necessary for the per¬ 
fect, complete and convenient operation and maintenance, to- 
the entire satisfaction of the Chief of the Bureau of Yards and 
Docks.” 

Paragraph 9. Time of completion. —“The dock proper shall 
be entirely completed and ready for test in every respect and 
particular within twenty-seven calendar months from the date 
of the contract.” 

Paragraph 23. Plans and specification. —“General Plans in 
sufficient detail to give the Bureau a perfect understanding of 
the design of the dock, its method of operation, manipulation 
and construction, and of the character and distribution of all 
material, machinery and appliances shall be furnished bv bid¬ 
ders. The general plans shall be accompanied by a specifica¬ 
tion, stress diagrams and calculations in further amplification 
of the design and its capabilities, with full explanations of all 
operations and manipulations. The character and make of all 
machinery and appliances shall be described in the specifica¬ 
tion, and all other details necessary to enable the Bureau to 
arrive at a correct and perfect understanding of what is pro¬ 
posed. The contractor shall furnish the Bureau with tracings 
of all general plans.” 

Paragraph 24. Detail plans. —“The contractor shall prepare 
detail plans in amplification of general plans showing all parts 
of the dock and its appliances. Triplicate blue prints of these 
plans shall be submitted to the officer in charge for examina¬ 
tion and approval before any work is performed. Tracings 
of approved plans shall be furnished to the Bureau. Approval 
of detail plans shall be of a general nature, and shall not relieve 
the contractor from errors, discrepancies or omissions that may 
occur therein, which shall be remedied or supplied whenever 
discovered or required.” 

Paragraph 30. Work to be done by the Government. —“The 
Government will do all the necessary dredgmg at the final lo¬ 
cation of the dock.” 

Paragraph 31. Location, —“The location of the dock is at 
the Naval Station, Cavite, P. I., at a site to be selected, but the 



FLOATING DRYDOCKS. 


31 


Government reserves the right reasonably to vary the location, 
as may be to its best interests, before the final acceptance of 
the dock. The contractor shall provide moorings, approaches 
and other necessary accessories and appurtenances suitable 
for the location finally selected by the Government.” 

Paragraph 32. General description .—“The dock in general 
shall be an open-hearth steel structure, so designed and ar¬ 
ranged as to be readily self-docking without the aid of divers 
or auxiliary constructions. It shall be self-contained as to the 
operating machinery, and capable of being towed from place 
to place safely .without auxiliary bracing. It shall be of the 
general type, composed of watertight side walls and body or 

pontoons, with a general 1_1 shaped cross section, and 

divided into sufficient watertight compartments to give great 
stability, there being not less than six transversely. Simplicity 
and certainty of operation and freedom from possible disable¬ 
ment in all operations shall be given careful consideration by 
designers.” 

Paragraph 33. Length .—“The dock shall not be less than 
500 feet long over all, none of which length shall consist of 
bracketed platforms without lifting power.” 

Paragraph 34. Width .—“The dock shall have a clear width 
between fenders of not less then 100 feet.” 

Paragraph 35. Height and draught .—“The decks of side 
walls shall have not less than eight feet of clear height above 
the water, with 30 feet draught over 4-foot keel blocks.” 

Paragraph 36. Lifting capacity .—“The dock shall have a 
lifting capacity of not less than 16,000 gross tons, uniformly 
distributed over the entire length, with the main deck not less 
than two feet above the water, and with not less than one foot 
of water in the compartments.” 

Paragraph 37. Unit stress .—“No portion of the dock, or its 
connections, shall have a stress of more than 10,000 pounds 
per square inch under the specified loads, or 15,000 pounds per 
square inch in self-docking, with a wind pressure of thirty 
pounds per square foot of exposed surface.” 

Paragraph 38. Shiploads .—“The dock shall be designed to 







32 


FLOATING DRYDOCKS. 


dock all classes of vessels of the United States Navy, either 
centrally or with the center line of the keel I foot off the 
center line of the dock, with a freeboard of 2 feet, and shall 
provide for bearing over the full length of the dock. Dia¬ 
grams of weights, as far as available, will be furnished on ap¬ 
plication.” 

Paragraph 39. Distribution of load. —“The dock shall be 
so designed that the entire weight of a battleship may be safely 
carried by the main keel blocks, or one-half the weight on 
each line of docking keel blocks in whichever position the ship 
may be docked. The side walls shall be designed to take shor¬ 
ing at any point that may be necessary.” 

Paragraph 40. Working deck. —“The working deck of the 
dock shall be flush plated and so strengthened that docking 
keel blocks may be placed in any position.” 

Paragraph 41. Uniform pumping. —“The dock shall be so 
designed that the specified unit stress shall not be exceeded 
when the dock is pumped uniformly from all compartments to 
a freeboard of 2 feet with any specified ship load docked cen¬ 
trally.” 

Paragraph 42. Allowable deflection. —“With any specified 
ship load docked centrally and all compartments pumped uni¬ 
formly until the dock has a freeboard of 2 feet, the longitu¬ 
dinal and lateral deflection over the entire working deck of 
the dock shall not exceed 1 in 2,000. Within the limits of al¬ 
lowed deflection the ship load shall lie assumed to be perfectly 
flexible.” 

Paragraph 43. Keel blocks. —“All keel blocks shall be of 
clear heart oak, of a uniform length of 5 feet, a width of 16 
inches and planed to a uniform thickness of 12 inches so as 
to be interchangeable.” 

Paragraph 44. Spacing of blocks. —“Main keel blocks shall 
be spaced 2 feet on centers, and docking keel blocks 4 feet on 
centers.” 

Paragraph 45. Block-sills. —“Docking keel blocks shall rest 
on sills of clear, heart, long-leaf yellow pine, 16 inches wide 
and planed to a uniform thickness of 12 inches, so as to be in- 






FLOATING DRYDOCKS. 


33 


terchangeable. I he sills shall be of sufficient length to accom¬ 
modate all the docking keels in the Navy.” 

Paragraph 46. Sliding blocks.—" Every third sill shall be 
fitted with a sliding block, and shall extend to within 2 feet of 
the main blocking and sufficiently outboard so that the blocks 
cannot be hauled off the sills.” 

Paragraph 47. Drainage. —“Athwartship and fore-and-aft 
drainage shall be provided on the working deck of the dock.” 

Paragraph 48. Side wall decks. —“The decks of side walls 
shall have a clear passage fore and aft of not less than 5 feet 
in width. They shall have a hand-rail on the outboard side 
and a 12 by 16-inch clear, heart, yellow-pine timber on the 
inside, fitted with fair leads and cleats.” 

Paragraph 49. Passage. —“Passage from one side wall to 
the other shall be provided.” 

Paragraph 50. Communication .—“Telephone or speaking- 
tube communication shall be provided from one side wall of 
the dock to the other, along the side walls, and to the engine 
rooms.” 

Paragraph 51. Headline. —“Provision shall he made for a 
central headline and for hauling the same from side walls.” 

Paragraph 52. Capstans, winches and bitts .—“There shall he 
not less than four capstans on each side wall and the necessary 
capstans or winches for handling moorings. There shall he 
not less than eight bitts on each side wall.” 

Paragraph 53. Moorings. —“Two sets of moorings shall 
be provided at each corner of the dock.” 

Paragraph 54. Runways and shoring stages. —‘“Two lines of 
runway and shoring stages not less than 36 inches wide shall 
be provided on the inner side of each side wall, and a runway 
about 2 feet above the main deck.” 

Paragraph 55. Ladders and steps. —“Access shall he had to 
the runways and shoring stages by suitable ladders and steps 
from the top of side walls and main deck.” 

Paragraph 56. Fenders. —“All parts of the dock liable to 
be fouled by a ship in docking shall be fitted with heavy rub¬ 
bing timbers and fenders, so arranged as to not injure the dock 

3 









34 


FLOATING DRYDOCKS. 


if carried away and to be readily replaceable. The exterior of 
the dock shall be fitted with timbers and rubbing fenders as 
a protection from drift and fouling.” 

Paragraph 57. Fire service.—“A fire service and washing- 
down system shall be provided the entire length of each side 
wall at or near the top, and with not less than four hose con¬ 
nections on each side." 

Paragraph 58. Indicator system .—“The dock shall be fitted 
with a reliable pneumatic or hydraulic indicator system to show 
the depth of water in all compartments at all times.” 

Paragraph 59. Levels and gauges .—“The dock shall be fitted 
with levels and gauge boards to indicate the trim.” 

Paragraph 60. Height of self-docking .—“When self-docked 
all under-water portions shall be raised to a clear height of not 
less than 5 feet, and shall be safely and readily accessible for 
inspection, painting and repairs." 

Paragraph 61. Self-docking connections .—“With the dock 
at light-draught line, all self-docking and strain transmission 
connections shall be above water.” 

Paragraph 62. Power .—“The dock shall be operated by 
steam power, and shall be fitted with the necessary boilers, en¬ 
gines, pumps, feed-water heaters, steam separators and other 
accessories desirable to make a first-class self-contained plant.” 

Paragraph 63. Boilers and engines .—“There shall be not 
less than 600 nominal horsepower of boilers and engines suita¬ 
bly distributed to give the best results. Simplicity and cer¬ 
tainty of action and freedom .from possible breakdowns in 
operation are to be given the first consideration. Engines of 
a type and style which will produce the least vibration in the 
side walls are desired." 

Paragraph 64. Main pumps .—“If of the centrifugal variety, 
the main pumps shall have a discharge of not less than 16 
inches, and an equivalent discharge for other varieties.” 

Paragraph 65. Piping .—“All piping shall be of ample size 
to supply the pumps at maximum speed, and so installed as to 
be readily accessible for repairs or renewal.” 

Paragraph 66. Valves .—“The piping and flow of water shall 






FLOATING DRYDOCKS. 


35 


be completely controlled by a system of simple and durable 
bronze-mounted valves, of the wedge variety, of easy and 
certain operation. All valves shall be fitted with indicators.” 

Paragraph 67. Fuel and water. —“Storage shall be provided 
for fuel and fiesh water sufficient for two complete successive 
dockings of the maximum load.” 

Paiagiaph 68. Connections to ship. —“Provision shall be 
made for supplying a ship in dock with water and for carrying 
off her waste water and sewerage.” 

c!> 

Paragraph 69. Machine shop. —“A small machine shop, suit¬ 
able for light repairs to the dock, shall be installed in one side 
wall.” 

Paragraph 70. Store room and quarters. —“Such portions of 
the side walls above the engine decks as are not occupied by 
machinery shall be fitted as store rooms, and as quarters for 
the dock’s officers and crew, with suitable mess arrangements.’^ 

Paragraph 71. Hatches, skylights, deadlights and ladders .—v 
“I he side walls shall be fitted with all the necessary hatches,, 
skylights, deadlights, ladders and other conveniences necessary 
or desirable.” 

Paragraph 72. Lighting plant .—“An electric light plant shall 
be installed on the dock for lighting all interior working and 
storage compartments and with connections for portable lights 
on the dock.” 

Paragraph 73. I entilating system .—“A blower system shall 
be installed for ventilation of all working and storage spaces 
and quarters in the dock.” 

Paragraph 74. Time of operation .—“The dock shall be de¬ 
signed to lift a load of 16,000 gross tons with a draught of 30 
feet clear of the water in four hours. Lighter loads of less 
draught shall be lifted in a correspondingly shorter time, and 
the pumps shall readily operate under a head of 35 feeff The 
time of operation shall be reckoned from when the ship has 
taken the blocks and shores and pumping is commenced until 
the keel is out of water.” 

Paragraph 75. Place of tests. —“All docking and self-dock- 





3 6 


FLOATING DRYDOCKS. 


ing tests shall be made at a suitable and convenient place at or 
near the works of the contractor." 

Paragraph 76. Preliminary tests. —“Preliminary tests in 
sinking and raising the dock shall be made by the contractor 
to satisfy the officer in charge that the dock is in perfect work¬ 
ing order.” 

Paragraph 77. Cruiser test. —“The dock shall be tested in 
docking a cruiser furnished by the Government centrally or 
off line as specified.” 

Paragraph 78. Battleship test. —“The dock shall be tested in f 
docking a battleship furnished by the Government centrally 
or off line as specified.” 

Paragraph 79. Deflections .—“Observations shall be made 
for deflections and permanent set during the dockings by 
specially designed instruments furnished by the contractor 
which will become part of the dock’s outfit. In determining 
the final deflection allowance shall be made for permanent 
set and temperature deflections, and the blocking shall be 
straight.” 

Paragraph 80. Self-docking tests .—“The dock shall be com¬ 
pletely self-docked upon the completion of the docking tests.” 

Paragraph 81. Board of tests. —“The tests shall be conducted 
by a board of naval officers appointed by the Secretary of the 
Navy, one of whom shall be a line officer expert in steam 
engineering, one a naval constructor and one a civil engineer. 
The dock will be carefully examined by the Board and tested 
for all specified requirements.” 

Paragraph 82. Conduct of tests .—“In docking naval vessels 
the ships shall be maneuvered, entered and placed in position 
in the dock by the commanding officer and the naval construc¬ 
tor of the Board, according to naval practice, with tugs and 
labor furnished by the contractor. All preparations and manip¬ 
ulations of the dock in testing shall be conducted by the con¬ 
tractor to the satisfaction of the Board. A mutual understand¬ 
ing and agreement shall be had between the Board and con¬ 
tractor preceding docking tests, to prevent accidents to the 
ship or dock.” 




FLOATING DRYDOCKS. 


37 


Paragraph 83. Duration of battleship test.— 'On the last test 
the battleship shall be carried centrally on the dock for forty- 
eight hours without the dock showing any undue signs of 
strain or fatigue.” 

Paragraph 84. Condition on delivery .—“If the dock is de¬ 
livered by the contractor at Cavite, all machinery, valves, strain 
transmission and self-docking connections shall be put in per¬ 
fect working order before the dock is turned over to the Gov¬ 
ernment.’' 

Paragraph 85. Docking material .—“All the necessary ma¬ 
terial and appliances needed in testing and operating the dock 
shall be supplied by the contractor and become part of the 
dock’s outfit.’’ 

Paragraph 86. Dock equipment .—“The dock shall be pro¬ 
vided with all conveniences for operation, manipulation and 
self-docking.” 

Paragraph 87. Boats .—“Two 20-foot metallic life boats with 
complete equipment shall be provided with the dock.” 

Paragraphs 88-100. Provide for the quality of materials 
and their inspection. The steel is required to be open-hearth 
of a superior quality, and of a medium grade for the hull 
material and a soft grade for the rivets. 

Paragraphs 101-113. Provide for the quality of workman¬ 
ship and its inspection. Workmanship must be neat and work¬ 
manlike and equal to the best American ship practice. 

Paragraphs 114-118. Provide for cleaning and painting 
metal. 

Bids were asked under five items, as follows: 

Item 1. For delivery at Cavite. 

Item 2. For delivery at the works of the contractor insured 
for towing. 

Item 3. For delivery at works of contractor without insur¬ 
ance. 

Item 4. For towing to Cavite. 

Item 5. For alternate proposals at the discretion of bidders. 



FLOATING DRYDOCKS. 



REVIEW OF SPECIFICATION. 

The specification is the most comprehensive and complete 
of any that has yet been issued for a floating drvdock. 

Heretofore the designs for floating drydocks for Naval 
purposes have been largely left in the hands of civilian de¬ 
signers whose principal business is in designing commercial 
docks. The English naval architects have, practically, had a 
monopoly of this line of naval architecture for the past twenty- 
five years, and such developments as have been made up to 
the present time have been made by them. Too much of purely 
commercial consideration has entered into the design of mili¬ 
tary docks. There has been an effort to secure the greatest 
possible dimensions and displacement with the least amount of 
material and call this result battleship lifting power. 

The design of a military floating drvdock should differ as 
much from that of a commercial floating drydock as the design 
of an armored cruiser differs from that of a transatlantic liner. 
The uses and purposes are as different in one case as in the 
other. The commercial dock deals with ships having strong 
bottoms, much inherent stiffness, and weights of fairly uniform 
distribution. The military dock deals with ships having ten¬ 
der bottoms, less stiffness, and great weights unevenly dis¬ 
tributed. In the commercial dock, original cost and interest 
on the investment have first consideration. In the military 
dock, strength, safety, durability, ease and certainty of opera¬ 
tion, and adaptability to varying conditions take precedence 
over all else. A battleship is not designed to yield a certain 
return in money, and neither should a military dock be so 
designed. 

The aim of the specification is apparent from the quota¬ 
tions previously given. In designing a floating dock, both 
present and future conditions must have consideration, and 
developments anticipated or unexpected must be provided for. 
In our own naval establishment a definite maximum seems to 
have been reached for the present. Battleships of 16,000 
tons displacement and 450 feet of length, and armored cruisers 
of 14,500 tons displacement and 500 feet in length will ap- 




FLOATING DRYDOCKS. 


39 


parently be our standard for some years to come, and it is an 
open question among naval experts whether future conditions 
will increase or diminish these figures. Radius of action, ac¬ 
cessibility to all ports of commercial or strategic importance, 
improvements in arms, armament and machinery, speed, and 
durability in action are some of the factors influencing the di¬ 
mensions and displacement of a fighting ship. The present 
specification provides for a floating dock which will not only 
take with ease all our present naval vessels, but will also safely 
dock a battleship of 20,000 tons displacement, or an armored 
cruiser of 600 feet in length. In the present specification the 
draught of the dock has had especial consideration. An ordin¬ 
ary working draught of 30 feet has been provided with an 8- 
foot freeboard of the side walls, and it has been further pro¬ 
vided that the pumps shall readily operate under a head of 35 
feet. This would, in emergency, allow a draught over the 
keel blocks of 36 feet. 

A draught of 30 feet is a liberal estimate for future war¬ 
ships. A military dock, however, may be called upon to deal 
with ships considerably down by the head or stern, or badly 
listed, and ample provision has been made for such contin¬ 
gencies. 

The limits of stress and deflection and the uniform pumping 
and lifting capacity provided in the specification will give a 
dock in which a ship may be docked in the end, or in which 
the ship may be straightened or hogged as required, by regu¬ 
lating the water load in the compartments of the dock. The 
value of these conditions for many repairs to hull and ma¬ 
chinery is very great. 

The equipment of the dock as to the conveniences for opera¬ 
tion for the safe and convenient docking of vessels has been 
made full and complete. 

The preservation of a large steel floating dryclock necessi¬ 
tates that it shall be self-docking. [hey are far too laige to 
enter a graving dock, and, even, if it were possible, they ai e fre¬ 
quently located where no graving docks exist 01 aie possible. 
For the greatest safety in docking a war vessel, a floating dock 


4 o 


FLOATING DRYDOCKS 


should be as nearly continuous and solid as possible. For 
self-docking, it must be separable into parts which will dock 
each other, thus permitting each section to be repaired when 
necessary. 

The problem, then, which confronts the floating-dock de¬ 
signer is to produce a structure which is practically solid and 
continuous in docking operations, but which can still be sepa¬ 
rated into parts and self-docked. The specifications have left 
the self-docking feature entirely free to designers, requiring 
only a safe and convenient height in self-docking and a limit 
of stress on material. 


THE BIDS. 

Bids on competitive designs under the general specification 
were received bv the Bureau of Yards and Docks, Navy De¬ 
partment, on March 14, 1903. 

Mr. Chauncey N. Dutton, Engineer, submitted bids on a 
modification of his pneumatic lift-lock system. The apparatus, 
while of great merit, provided a stationary instead of a mova¬ 
ble dock, and placed the responsibility of foundations on the 
Government. 

The United States Shipbuilding Company submitted bids 
on a Rennie type of dock, as follows: 

For delivery at the Cavite Naval Station, to be constructed 
at San Francisco and towed out, or erected and launched at 
the Cavite station, in the discretion of the bidders, $1,443,000. 

For delivery to the Government at San Francisco, unin¬ 
sured, $1,220,000. 

For delivery to the Government on the Atlantic Coast, un¬ 
insured, $1,184,000. 

For delivery to the Government at Cavite Station, “knocked 
down,” and to be erected and launched by the Government, 
$1,100,000. 

The Maryland Steel Company submitted bids on a Clark 
type of dock, on a type proposed by Civil Engineer A. C. 
Cunningham, U. S. N., and on a type of their own design, as 
follows: 


FLOATING DRYDOCKS. 


4 r 

Clark type, delivered on the Atlantic Coast, uninsured, 
$i, 2I 5 , 00 °- The general plan of the design is shown in the 
sketches accompanying the description of the dock. 

Cunningham type, delivered on the Atlantic Coast, unin¬ 
sured, $1,164,000. 

Maryland Steel Company type, delivered on the Atlantic 
Coast, uninsured, $1,124,000. 

Cunningham type, in 452 feet length, delivered on the At¬ 
lantic Coast, uninsured, $1,085,000. 

THE AWARD. 

On April 9, 1903, the contract was awarded to the Maryland 
Steel Company on their own design at the price bid. 

THE DESIGNS. 

The design of Mr. Dutton not being for a floating dock will 
not be reviewed here. 

U. S. SHIPBUILDING COMPANY'S DESIGN. 

The design is on the Rennie type of dock, and was made for 
the bidders by Stevenson & Company of England. It is well 
illustrated in the accompanying plates. This type of dock 
was proposed by Rennie, the English drydock expert, many 
years ago. It was well suited to its time when ships were 
much shorter and stiffer than they now are, and had much 
less heavy and concentrated loads. As a military dock it has 
passed its period of usefulness. It is dependent upon its side 
walls almost entirely for longitudinal stiffness on account of 
its numerous transverse pontoons. The pumps are located un¬ 
desirably high for certainty of action in removing the last of 
the water from the pontoons. 

This type of dock is not regarded with favor for towing 
long distances, as it has little resistance to torsion, and is easily 
twisted in a sea way. Self-docking in a strong tide or current 
is not easy on account of the pontoon coming out sideways 
from under the walls. When one or more intermediate pon- 


42 


FLOATING DRYDOCKS. 


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Proposed Self-Docking Steel Floating Drydock for U. S. Naval 
Station, Cavite, Philippine Islands. 


U. S. Shipbuilding Company Design, Rennie Type. 

Details of connections between pontoons and side walls, and method of 
tiffening bottom chord of side wall at junction of pontoons. All bolts and 
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Sectional Elevation 




Proposed Self-Docking Steel Floating Drydock for U. S. Naval Station, Cavite, Philippine Islands. 

United States Shipbuilding Company Design, Rennie Type. 

(i f Sectional elevation through pontoons, showing port side wall from inboard, starboard side wall remo\ed. The side walls are similar. 

( 2 ) Plan of dock, showing general distribution of machinery in side walls and location of blocking and sills on decks of pontoons. Location of girders and bulkheads indicated by dotted lines. 


Face p. 42—c. 




















































































































































































































































































































































































































































































































































































































































































































B. 




Proposed Self-Docking Steel Floating Drydock for U. S. Naval Station, Cavite, Philippine Islands. 

U. S. Shipbuilding Design, Rennie Type. 

Cross sectional elevation, side sectional elevation and sectional plan, showing location of machinery and pumps and arrangement of piping and valves. The installation is similar on 
each side of the dock. In the cross section the main pipes are shown on one side and the drainage pipes on the other. In the plan the main and drainage pipes are shown on one side and 
the air pipes on the other. 


Face p. 42—d. 












































































































































































































































































































































































































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FLOATING DRYDOCKS. 


43 



U. S. Shipbuilding Co. Design, Rennie Type. 
Cross section showing piping. 


MARYLAND STEEL COMPANY’’S DESIGNS. 

The Clark Type .—This design was made for the Maryland 
Steel Company by Mr. Lyonel Clark, of London, whose design 
for the New Orleans military dock was described in the preced¬ 
ing issue of this Journal. 

This design is the best of its type yet produced by Mr. Clark. 
The submerged joints have been brought above the water line, 


Proposed Self-Docking Steel Floating Drydock for U. S. Naval 

Station, Cavite, Philippine Islands. 

U. S. Shipbuilding Company Design, Rennie Type. 



Rennie Type of Drydock. 

Swinging bridges open, showing system of fenders around body of dock, 
and arrangement of ladders and location of towing bitts. 













































































































































44 


FLOATING DRYDOCKS. 


and in nearly every particular the specified requirements have 
been met. The altars, which are necessitated by the upper 
connections, considerably reduce the area of the working deck, 
and narrow its clearance for a considerable height above the 
blocking. The pumps are, necessarily, placed higher than de¬ 
sirable, and in securing the specified self-docking of the side 
walls the dock is canted to a very undesirable angle, and a por¬ 
tion o,f the main deck is submerged. The self-docking of the 
pontoons in this type is also illustrated in the preceding number 
of this Journal. Other modifications of this dock are as 
shown by the plans, which are from the designs for a dock con¬ 
structed by Mr. Clark for a foreign government. 

The Cunningham Type .—This design was made by the 
Maryland Steel Company on a type proposed by the author 
of this paper. It is well illustrated by the titles and sketches, 
which are sufficiently complete to point out their distinctive 
features in the accompanying plates. 

In this design the bidders state in their detailed specifica¬ 
tion as follows: 

GENERAL DESCRIPTION. 

“The dock will be a self-docking, floating steel structure, 

composed of side walls and pontoons, with a general 1_i 

shaped cross section, divided into three sections and fifty-four 
watertight compartments, and so arranged that each section 
can be readily self-docked by means of the others without the 
aid of auxiliary constructions. 

“ The dock will have a total length of 500 feet, a clear width 
between fenders on side walls of 100 feet, and a freeboard of 
11 feet with 30 feet of water above the keel blocks. 

“The lifting capacity will be 16,000 gross tons, or 32 tons 
per running foot over the entire length of the dock, with main 
deck 2 feet above water line and 1 foot of water remaining 
in all compartments. 

“It will be divided into three uniform sections, strongly 
bolted together, and each section will be independent and con¬ 
tain its own operating machinery. Each pontoon is divided 




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FLOATING DRYDOCKS. 


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46 


FLOATING DRYDOCKS. 


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Sei.f-Docking Steel Floating Drydock, Pola Type, Clark Design. 






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Self-Docking Steel Floating Drydock, Pola Type, Clark Design. 


FLOATING DRYDOCKS 



Views showing self-docking of center and end sections. 






































FLOATING DRYDOCKS. 


49 


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50 


FLOATING DRYDOCKS. 



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Proposed Self-Docking Steel Floating Drydock for U. S. 

Naval Station, Cavite, Philippine Islands. 

Maryland Steel Company Design, Cunningham Type. 

Half end view of dock section showing connection for bolts, and 
section through same showing manner of bracketing back into body 
of dock. 

into eighteen watertight divisions, each compartment being 
provided with a separate pipe for pumping. 

“The pumping machinery will be located in the port side 
wall with the main drain pipe at bottom of same and branches 
leading to the different compartments. 

“The controlling valves will be operated from each engine 
room, and an operating house will be located on the top deck, 
with speaking tubes leading to the engine rooms, so that the 
operator in charge can at all times control the operation from 
the operating house, and, by means of indicators, fitted above 











































































































FLOATING DRYDOCKS. 


51 


each engine room, see how all the valves are being regulated. 

‘'In the operating house will also be located an indicator 
system showing the depth of water in all the compartments. 

“The main pumping system to consist of three horizontal, 
direct-connected, compound engines, and steam will be fur¬ 
nished by three water-tube boilers. These pumps are suffi¬ 
ciently large to easily raise the structure within the time limit 
prescribed. 

“An auxiliary boiler will provide steam for all the auxiliary 
machinery on the starboard side, such as capstans, electric 
plant, distilling plant and machine shop. 

“On the side-wall decks will be located eight steam capstans 
and necessary bitts and fairleads for handling of lines when 
taking ships in and out of the dock. 

“A combined fire service and washing-down system is pro¬ 
vided for protection of both ship and dock from fire, and the 
washing-down system will greatly facilitate the cleaning of 
ships when docked. 

“The dock will be moored by two sets of heavy anchors, and 
chain cables at each corner fastened to heavy bitts, leaving the 
dock free to sink and rise to the required depths in docking the 
vessel. 

“The ship to be supported on three lines of blocking, the 
center line of keel blocks to be 2 feet centers, extending the 
whole length of the dock, and the side lines or docking keel 
blocks to be spaced 4 feet centers, and to extend fore and aft 
over a length, of 280 feet. 

“The general features and all details entering into the de¬ 
sign of this dock, both for the support of the ship, the opera¬ 
tion of the dock, and the method of self-docking as described 
in the following specifications, are believed to fully meet the 
present and future needs of the naval service foi safe docking 
all the present and to date projected ships of the United States 
Navy not over 16,000 tons displacement. 

“The general arrangement of the dock is shown on Plan 

No. 1. 

“Attention is particularly called to the fact that, with the 


52 


FLOATING DRYDOCKS. 


bolted sectional type, the 500-foot dock can at any time in the 
future be increased to about 666 feet in length by constructing 
a new intermediate section and adding it to the dock. 

“This new section would be an exact duplicate of the present 
intermediate section, and during its construction the dock 
would continue in use to the time that the new section was 
ready to be installed in place. The installation of the new 
section would be accomplished in a few days, when the dock 
would be again ready for operation on an enlarged scale. 

“With the increased length of the dock secured by the ad¬ 
dition of a second intermediate section, it would no longer be 
desirable or necessary to employ uniform pumping for the 
loads for which the dock is at present designed. The actual 
lifting capacity of the dock would be increased to 24,500 tons, 
and when such load came upon the dock it would be so dis¬ 
tributed as to give a correspondingly increased bearing, so 
that little or no pumping of the unloaded compartments would 
be required. 

“With the limit of unit stress employed in the present dock 
and the small deflection permissible, the increased length re¬ 
sulting from the addition of a new intermediate section would 
still leave a dock in which no undue strains or deflection would 
occur when handled with moderate intelligence and judgment 
by the dock master. 

“This increase of length would bring a bolted section at 
the center of the dock where the greatest bending occurs, but 
additional intermediate flanges can be installed and bracketed 
back into the structure if it is desired to make this central joint 
unusually strong.” 


METHOD OF SELF-DOCKING. 

“ In self-docking the center section of the dock the water is 
first pumped down uniformly as low as practical in all the 
compartments with the drainage service. Water is then ad¬ 
mitted freely to all compartments on the starboard side out¬ 
board of the starboard intermediate bulkhead, until the dock 


FLOATING DRYDOCKS. 


53 


is heeled over sufficiently to bring the main drainage pipe on 
the port side well above water. 

“The inner valves on the main drain pipe will be closed, and 
the drain pipe connections between the sections are then dis¬ 
connected and removed. The water in the starboard compart¬ 
ments is now removed by the main pumps and the dock is 
emptied with the drainage pumps until light water line, about 
6 feet, is reached and all the joint angles and bolts are above 
water. The drainage and fire mains are also to be discon¬ 
nected on both sides. The connection bolts are then removed, 
except a few friction bolts in slotted holes on each side, which 
are loosened up gradually until each section reaches its own 
floatation, or, if found necessary, water is admitted until an 
equal balance is obtained. The remaining friction bolts are 
now taken out, leaving the pontoons floating independent of 
each other, held in position by hawsers. 

“Thereafter, the water is admitted freely to all compartments 
in end pontoons Nos. i and 3 until a draught of 21 feet 5 
inches is reached, and all three sections are brought together 
until slotted holes are fair with round holes and friction bolts 
are entered. Drift pins may now be inserted in round holes, 
and sections trimmed until all flanges bear and all holes are 
fair, after which all bolts are inserted and tightened up. The 
dock is now ready for lifting, and the water is pumped out 
of both end pontoons until the center pontoon has a draught 
of about 6 inches. At this stage the mud valves in the center 
pontoon are opened wide, permitting the remaining water to 
drain out of the center pontoon as the lifting progresses. 

“In pumping the end pontoons the twelve compartments 
nearest to the center pontoon are pumped down to about 2 
feet, and the six extreme end compartments in each end section 
are drained down to about 3 feet. The dock will then be 
found at a draught giving 5 feet in clear height between the 
water line and the bottom of the center pontoon. The bottom 
of the center pontoon can then be inspected, cleaned and painted 
or repaired from floats, all parts of the pontoon being easih 

accessible. 


54 


FLOATING DRYDOCKS. 


“In lowering the center pontoon all mud valves are closed 
and water is admitted freely to all compartments in the end 
pontoons until a draught is reached at which the center pon¬ 
toon will float and all three sections are at a balance. All bolts 
in the joints are now removed except friction bolts in slotted 
holes, which are loosened gradually until each section slips to 
its own floatation. If a tendency of unequal balance is noted, 
water is admitted to overcome it, leaving the sections again 
floating independent of each other. The water in the end pon¬ 
toons is now pumped out by the main pumps, and if necessary, 
by the drainage pumps until light water line is reached. 

“If the stern pontoon, No. 3, has to be docked next, a 
hawser is passed from No. 1 to No. 3 on the outside of pon¬ 
toon No. 2, which pontoon is now moved out sideways by means 
of a tug or kedge anchors and hawsers. When pontoon No. 
2 is out of line a second hawser is passed between pontoons 
Nos. 1 and 3. The stern-anchor cables are now slipped, the 
ends being made fast to two buoys by suitable lines. No. 3 
pontoon is now warped up close to pontoon No. 1, and No. 2 
is placed in the position formerly occupied by No. 3. 

“The same method is now used in docking the stern pon¬ 
toon, No. 3, between the other two pontoons, No. 1 and No. 
2, as previously described in docking the center pontoon. 
After the stern pontoon, No. 3, is again afloat, the bow pontoon. 
No. 1, is handled in the same manner, and when the self-dock¬ 
ing is finished the pontoons are once more shifted into their 
original positions. All joints are bolted up and drainage and 
fire systems also connected. The dock is then heeled to star¬ 
board, the main drain-pipe connections on the port side again 
inserted, the water on the starboard side pumped out by the 
main pumps, and the dock is again floating in complete working 
order.” 

The method of self-docking is illustrated quite plainly in 
accompanying sketches. 






Proposed Self-Docking Steel Floating Drydock for U. S. Naval Station, Cavite, Philippine Islands. 

Maryland Steel Company Design, Cunningham Type. 

(1) Elevation of starboard side wall from outboard, showing junction of sections, location of decks and bulkheads, and location of auxiliary machinery in bow, and quarters in steru-. 

(2) Plan showing location of main pumping machinery in port side wall, arrangement and distribution of piping, and location of girders and bulkheads in body of dock. 

(3) Sectional elevation of port side wall from inboard, showing location and distribution of machinery, pumps and valves. 


i 


Face p. 54. 

































































































































































































































































































































































































































































































































































































































































































































































FLOATING DRYDOCKS. 


55 


THE MARYLAND STEEL COMPANY TYPE. 

This type was especially developed by the Maryland Steel 
Company to meet the conditions of the specification. 

Of this design the builders state in their detail specification 
as follows: 


GENERAL DESCRIPTION. 

• “The proposed dock will be a self-docking, floating, steel 
structure, composed of side walls and pontoons with a general 

I_i shaped cross section in three divisions, and so arranged 

that all three sections of the dock can be readily self-docked 
by means of the others without aid of auxiliary constructions. 

“The dock will have a total length over all of 500 feet, a 
clear width between fenders on side walls of 100 feet, and a 
freeboard of 11 feet with 30 feet of water above the keel 
blocks. 

“The lifting capacity will be 16,000 gross tons or 32 tons 
per running foot over the entire length of the dock with the 
main deck 2 feet above water line and 1 foot of water remain¬ 
ing in all compartments. 

“The dock is divided into three parts, one center pontoon, 
about 316 feet long, built solid into and between the two side 
walls which extend their full depth of 63 feet 6 inches over 
the entire length of the center pontoon, and at both ends are 
so arranged so as to overhang the end pontoons. The two 
end pontoons are each about 89 feet long and extend under the 
overhanging side walls, being strongly secured thereto by hori¬ 
zontal bolted connections. 

“Both end pontoons are provided with outside independent 
side walls, extending the full length fore and aft of each end 
pontoon, and of sufficient height to permit the end pontoons 
to be sunk and brought under the center pontoon when self¬ 
docking same. 

“Each end pontoon can be manipulated in self-docking by a 
small independent pump and engine located on the port side 
in each pontoon, and by all the necessary valve gearing placed 



Accepted Design Seef-Docking Steed Floating Drydock for U. S. Navae Station, Cavite, Phieippine Iseands. 

Maryland Steel Company Design and Type. 


56 


FLOATING DRYDOCKS. 



Plan showing self-docking of end and center sections. 




































































































































FLOATING DRYDOCKS. 


57 


in the center of each pontoon side wall on the port side for 
this purpose. 

“The end pontoons can be readily self-docked by lifting both 
at the same time on the deck of the center pontoon of the dock. 

“The center pontoon is divided into twenty-four, and each 
end pontoon into eighteen, watertight compartments, making 
a total of sixty watertight divisions, each compartment being 
provided with a separate pipe for pumping. 

“The main pumping machinery will be located in the port 
side wall, with the main drain pipe at the bottom of same and 
branches leading to the different compartments. 

“The controlling valves will be operated from each engine 
room, and an operating house will be located on the top deck, 
with speaking tubes leading to the engine room, so that the 
operator in charge can at all times control the operation from 
the operating house, and, by means of indicators fitted above 
each engine room, see how all the valves are being regulated. 
In the operating house will also be located an indicator system 
showing the depth of water in all the different compartments. 

“The main pumping system to consist of three 24-inch hori¬ 
zontal centrifugal pumps driven by three horizontal, direct- 
connected, compound engines, and steam will be furnished 
by three water-tube boilers. 

“If preferred, a pumping plant of equal capacity, consisting 
of two 30-inch horizontal centrifugal pumps driven by two 
horizontal, direct-connected compound engines, may be in¬ 
stalled, instead of the above three engines and pumps. 

“An auxiliary boiler will provide steam for all auxiliary 
machinery on the starboard side, such as capstans, electric 
plant, distilling plant and machine shop. 

“On the side-wall decks will be located eight steam cap¬ 
stans and necessary bitts and fairleads for handling of lines 
when taking ships in and out of the dock. 

“A fire and washing-down system is provided for the pro¬ 
tection of both ship and dock from fire, and the washing-down 
service will be found to greatly facilitate the cleaning of ships 
when docked. 


Accepted Drydock Design of Maryland Steed Company, Type for 

SELr DOCKING- STEEL FLOAT INO DOCK 


58 


FLOATING DRYDOCKS 



u 


Transverse section through central or main pontoon, showing location of machinery, pumps and piping. 








































































































































































































































































































FLOATING DRYDOCKS. 


59 


“The clock will be moored by two sets of heavy anchors and 
chain cables at each corner, fastened to heavy bitts, leaving 
the dock free to sink and rise to the required depths in dock¬ 
ing the vessel. 

“The ship to be supported on three lines of blocking, the 
center line or keel blocks to be 2 feet centers, extending the 
whole length of the dock, and the side lines or docking keel 
blocks to be spaced 4 feet centers and to extend fore-and-aft 
over a length of 280 feet. 

“The general features and all details entering into the de¬ 
sign of this dock, both for the support of the ship, the opera¬ 
tion of the dock and the method of self-docking as described 
in the following specifications, are believed to fully meet the 
present and future need of the naval service for safe docking 
all of the present and to date projected ships of the United 
States Navy not over 16,000 tons displacement. 

“The general arrangement of the dock is shown on plan 
No. 1. 

“Attention is particularly called to the fact that this type of 
dock possesses simplicity combined with great rigidity, having 
a solid center portion of great length and as short end pon¬ 
toons as practical. 

“As the divisions of the pontoons come considerably outside 
of the turrets in the heaviest battleships or cruisers of the 
United States Navy, the bending moment at this point is re¬ 
duced to nearly one-third of the maximum bending moment 
existing at the center of the dock when vessels of this class are 
docked. 

“Furthermore, the side walls are built solid, full depth into 
the whole length of the center pontoon and continuous above 
the deck of the end pontoons, being entirely free from joints 

or connections above this point. 

“Attention is further called to the simple method of self¬ 
docking the whole dock, comparatively few bolts in the con¬ 
nections requiring removal only once, and all three sections 
can be lifted and supported on blocking in the same manner as 
a vessel is docked. 


Accepted Design for Self-Docking Steel Floating Drydock. 


60 


FLOATING DRYDOCKS. 



Cross-section through end pontoon, showing supplementary side walls, chamber at end for location of operating machinery, 

apd connection at left between main side wall and end section, 































































































































































































Maryland Steel Company Design and Type. 

Plan showing location of pumping machinery in port side wall, distribution of watertight bulkheads and piping, and end sections in position, with dock ready for operation. 



Port 


Face p.—60. 


Accepted Self-Docking Steel Floating Dkydock for U. S. Naval Station, Cavite, Philippine Islands. 

Maryland Steel Company Design and Type. 

Sectional elevation through port side wall, showing location of pumping machinery and distribution of valves and pumps in center and end sections. 




















































































































































































































































































































































































































































































































































































































































































































































































- 




■ "9 











1 I 
























* 


. 

































































































FLOATING DRYDOCKS. 


6 l 

“In self-docking, no joints, or bolted connections whatever 
are subject to heavy strains or are required for docking the 
different sections, and as no delicate adjustments of water 
levels for careful manipulations for balancing the different 
sections are required, this type of dock can be quickly self- 
docked when handled with moderate intelligence and judgment 
by the dock master. 

“The side walls being continuous, communication is easily 
established throughout the entire length of the side walls, 
and simplicity and convenience being desirable features, the 
main boilers and engines have been concentrated in the center 
of the port side wall with the operating house directly above 
the pumping plant. 

METHOD OF SELF-DOCKING. 

“When self-docking the dock, the water is first pumped out 
as low as practical with the main pumps, and water is then 
freely admitted to all compartments on the starboard side out¬ 
side of the starboard intermediate bulkhead in the center pon¬ 
toon only until the dock is heeled over sufficiently to bring 
the main drainage pipe on the port side well above water. 

“The inner valves on the main drain will be closed, and the 
drain pipe connections between the pontoons are then discon¬ 
nected and removed. 

* 

“The water in the starboard compartments of the center pon¬ 
toon will be removed by the main pumps and the dock lifted 
to light water line. All anchor cables are now slipped, the 
ends being made fast to four buoys by suitable lines. For 
holding the dock in position lines are made fast to these buoys 
and lead up to the capstans on deck at ends of side walls. 

“Every other keel block to be removed, and the docking 
keel blocks will be adjusted so as to support the end pontoons 
under the transverse bulkheads. The top blocks will be capped 
with ordinary pine plank 3 inches by 12 inches spiked thereto 
for protection of the oak blocking. 

“The bolts in all connections between pontoons will now be 
removed and sufficient water admitted to the end pontoons 


62 


FLOATING DRYDOCKS. 


until a fair clearance is obtained between the connection angles. 
The end pontoons will then be warped out by the capstans and 
hawsers and turned around ready to enter the center pontoon 
between the side walls. The center pontoon is now sunk down 
to a depth sufficient to give about i foot clearance between the 
top of blocking and bottom of end pontoon, and the pontoons 
are warped in over the center pontoon and held centrally so 
that the docking keel blocking will come directly under the 
transverse bulkheads. 

“The center pontoon is now pumped up by the main pumps 
equally from all compartments until the deck is i foot or more 
above the water line. The bottom and the lower sides of the 
end pontoons can now be inspected, cleaned, painted or re¬ 
paired, all parts being easily accessible, with ample working 
spaces all around the pontoons. 

“While inspection of the bottom of the end pontoons is going 
on the blocking on the deck of the end pontoons shall be ad¬ 
justed so as to carry the center pontoon directly under all longi¬ 
tudinal bulkheads. Every other keel block will be removed, 
and all ton blocks will be capped by 3-inch by 12-inch pine 
planking. 

“The center pontoon will now be lowered by admitting water 
freely to all compartments until end pontoons are floating free, 
when they are warped out by the capstans between the side 
walls and held clear of the center pontoon, which is then 
pumped up to light-draught water line by the main pumps. 

“The end pontoons are now floated out, turned around and 
sunk down sufficiently to be warped under the center-pontoon 
side walls, water being admitted through the flushing valves 
in the end compartments. 

“The end pontoons will be held by hawsers in their original 
positions while water is again admitted, and the pontoons are 
lowered until the deck is about one foot above the water line. 

“The steam connection between the auxiliary steam pipes 
and the side walls is now made, the steam swinging joints 
giving perfect freedom for the pontoon to be moved as re¬ 
quired. 


FLOATING DRYDOCKS. 


63 


‘‘The end pontoons are now sunk until a clearance of about 
one foot between the blocking and the bottom of the center 
pontoon is obtained, and gradually warped under same. 

“As soon as both end pontoons are in proper position pump¬ 
ing is commenced by the 12-inch pumps in the end compart¬ 
ments and continued equally from all end pontoon compart¬ 
ments until the bottom of the center pontoon is 5 feet above 
water line. 

“The bottom of the center pontoon is now accessible for in¬ 
spection or repair, and all parts of the whole dock have been 
self-docked. 

“Inspection completed, the center pontoon will be lowered 
by admitting water freely to all compartments in both end pon¬ 
toons until afloat, when the end pontoons are moved to their 
original position and pumped up ready for connection to the 
center pontoon. 

“All connection bolts are now inserted and the dock heeled 
to starboard, the main drain-pipe connections on the port side 
again inserted, the water on the starboard side pumped out by 
the main pumps, and the dock is again floating in complete 
working order.” 

The method of self-docking is a development of existing 
designs. 

It will be noted that power is conveyed to the small end 
docks by a flexible connection. 

In this type of dock the width and length are functions of 
each other. The small end docks must have sufficient displace¬ 
ment to lift the main section. As the main section increases 
in length the end sections necessarily increase in length in or¬ 
der to have the displacement to lift it, and the main section 
must therefore be made wide enough to take the end sections 
on its deck. 

THE CUNNINGHAM TYPE IN 450 FEET LENGTH. 

This proposal is for a dock in all respects similar to the dock 
already illustrated, except in length. 

Of this proposal the bidders state as follows: 


6 4 


FLOATING DRYDOCKS. 


POSSIBILITIES OF THE BOLTED SECTIONAL DESIGN. 

“Especial attention is called to the bolted sectional dock of 
450 feet in length in connection with the possibilities of future 
lengthening of the structure. From the recent and latest de¬ 
velopments in battleships, it seems a fair assumption that 
the 450-foot.dock will supply all the bearing length and lift¬ 
ing power that will be needed for battleships for many years 
to come. It will more than supply the lifting power for ar¬ 
mored cruisers, whose length seems to have reached a stand¬ 
still for the present. As the 450-feet dock has more bearing 
length than is needed for the armored cruisers, it seems un¬ 
necessary waste of material to make a dock 500 feet long 
simply for the purpose of providing a working platform when 
the same can be much more economically obtained by the use of 
independent floating pontoons. 

“It is true that with all types of floating drydocks, except 
the bolted sectional type, it is wise to provide for future un¬ 
expected expansion in ships, as the other types of docks are 
either entirely unadaptable to expansion or can only be ex¬ 
panded at much cost and serious loss of time, and when ex¬ 
panded become comparatively weak and flexible structures. 

“Admitting, however, the possible desirability of expanding 
the 450-foot dock of about 17,000 tons lifting capacity to meet 
future conditions, the expansion is made to even greater ad¬ 
vantage than in the case of a 500-foot bolted sectional type. 

“The expansion is made by the addition to the structure of 
an intermediate section which is a duplicate of the others. The 
dock then reaches the length of about 600 feet and a lifting 
capacity of about 22,800 tons, which seems to be a requirement 
in excess of the developments in warships that are estimated 
on by the most radical minds. 

4 

“The indicated development of this 450-foot dock also pro¬ 
duces a structure in which the original conditions of unit stress, 
uniform pumping and deflection under loading are more closely 
preserved to the usual floating dock practice. 

“The dock desired by the Government in the Philippine 
Islands is of a type suitable for the heaviest ships. Such a dock 


FLOATING DRYDOCKS. 


65 


will necessarily dock all the smaller ships down to gunboats 
and torpedo craft. As, however, the Philippine Archipelago 
demands a fleet of the smaller type of gunboats for its most 
successful policing and protection, the largest size of floating 
dock, in ordinary types, would generally be operated at a great 
disadvantage in docking such craft. With the bolted sectional 
type, however, as here presented, each section is a complete 
and perfect floating dock in itself, and can be so used. The 
advantages of a separate and independent use of each section 
for the rapid and economical docking of a large number of 
small craft are obvious. 

“While it has no bearing on the present case, it seems de¬ 
sirable to call attention at this time to other possibilities of the 
bolted sectional type of dock. 

“The cross section in the dock has dimensions and lifting- 
power per foot of length which are more than ample for any 
development that will take place in warships for many years 
to come, and can therefore be regarded as a safe standard. 
Should the Government in the future provide itself with several 
floating docks of the bolted sectional type and of a standard 
cross section, the combinations of the sections of the various 
docks that could be made for emergencies and unexpected con¬ 
ditions are very numerous. Take, for example, two standard 
docks of three sections each. By simply combining these sec¬ 
tions we have at once a long four-section dock and a short 
two-section dock, or three short two-section docks. 

“The various useful combinations that can be made with 
three or four standard docks, especially where the intermediate 
sections are of high strength, are readily apparent and too 
numerous to mention here in detail.” 

An advantage of this type of dock is that the sections can 
be built and launched separately, and each section towed in¬ 
dependently if desired. 


THE POLA TYPE. 

In order that this paper may be a complete review of mili¬ 
tary floating docks to date, plates of a general plan and the 

5 


66 


FLOATING DRYDOCKS. 


method of self-docking of the Pola dock are presented here¬ 
with. 

This dock is being built by the Austrian Government for 
the Naval Station at Pola, and was designed by Mr. Lyonel 
Clark, of London, who designed the Clark dock previously 
mentioned, on which the Maryland Steel Company made a bid 
for the Cavite Naval Station. 

It will be noted that it is a bolted sectional design. The 
bolts are carried around through a special chamber and below 
the water line of the dock, and it is believed that it will be diffi¬ 
cult to keep them dry, and inconvenient to make and unmake 
the connection in self-docking operations on account of the 
flooding of the chamber. 

This type of dock can only be self-docked in smooth water, 
where there is little current. 

SUCCESS OF MILITARY FLOATING DOCKS. 

The success of the New Orleans military dock has carried 
this class of structure past the experimental stage. Its suita¬ 
bility for docking a first-class battleship was doubted by many 
experts, both naval and civilian, and its construction, voyage 
and test were matters of deep interest to the naval authori¬ 
ties of all maritime nations. 

The comprehensive and exacting requirements of the new 
specification placed the success of the Cavite military dock 
beyond question, and marks a new era in this class of naval 
architecture. 

Should the Government decide to tow r this dock to its des¬ 
tination with its own naval resources, a new and vastly import¬ 
ant maneuver will also have been added to naval practice. 



Floating Drydock “ Dewey.”—Dock Sunk Ready to Receive Ship. 























Floating Drydock “Dewey.”—U. S. Battleship “Iowa” Entering Dock. 









Floating Drydock “Dewey.”—U. S. Battleship “Iowa” Centered and Ready for Lifting. 








































FLOATING DRYDOCKS. 


6? 


TESTS OF THE CAVITE STEEL FLOATING DRY- 

DOCK.* 

By Civil Engineer A. C. Cunningham, U. S. Navy, 

Member. 


In the early part of June, 1905, the Maryland Steel Co. 
reported the Cavite self-docking steel floating drydock ready 
for test, having completed the same in one month’s less time 
than the twenty-seven allowed by the contract. 

As in the case of the Government floating dock at New 
Orleans, built by the same company, the Cavite dock was 
constructed in a shallow basin, and on completion the basin 
was flooded and the cofferdam at the entrance removed. While 
flooding the basin the valves of the dock were left open and 
the dock allowed to fill, so that it continued to rest on the 
pile and timber foundation on which it was built until the 
time selected for floating and towing it to the mouth of the 
Patuxent River, the place selected for test. 

When the dock rose from its timber bed it was christened 
the Dewey, after the Admiral of the Navy, by Miss Maud Endi- 
cott, the daughter of Rear Admiral M. T. Endicott, Chief 
of the Bureau of Yards and Docks, Navy Department, under 
whose administration the dock had been built, and who repre¬ 
sented the Navy Department when the dock was floated. 

In the preliminary test of the New Orleans floating dock a 
collier of 6,000 tons displacement was used. The increased 
confidence in this class of dock for warships, and in the Dewey 
dock in particular, is shown by the fact that one of the latest 
and heaviest ships, the armored cruiser Colorado, was selected 
for the preliminary test. 

* Reprinted by permission from Journal of the American Societ\ or Naval 
Engineers, Volume XVII, No. 3. 





68 


FLOATING DRYDOCKS. 


Before docking the Colorado , the dock was sunk to twenty- 
nine feet draught over the keel blocks and then pumped up 
light to a freeboard of two and one-half feet. The sinking was 
accomplished in one hour and thirty-six minutes and the 
pumping up in one hour and two minutes, showing that the 
dock is of very rapid action. On this test it was also demon¬ 
strated that little or no trimming was required, the dock sink¬ 
ing and rising practically level with all valves open. 

The U. S. S. Colorado was docked on June 23, 1905, having 
a displacement of 13,300 tons at that time. The main and 
docking keel blocks were all set at the same height. In this 
preliminary test no effort was made to secure speed, and one- 
half hour was used in making flushing and fire connections. 
The elapsed time from when the ship landed on the blocks 
until the keel came out of water was two hours and sixteen 
minutes. Pumping was continued until the dock had a uni¬ 
form freeboard of two and one-half feet, only enough excess 
of water being retained in the side walls and end compart¬ 
ments to give the necessary trim. The Colorado was car¬ 
ried on the dock about twenty-four hours without changing 
the water ballast. When the dock had reached a freeboard of 
two and one-half feet with the Colorado, the deflection on the 
main keel line in the five hundred feet of length of the dock 
was about one-quarter, of an inch; after about twenty-four 
hours the deflection in five hundred feet increased to about 
one and one-sixteenth inches. After undocking the Colorado 
the dock was found to have practically straightened without 
retaining any set. 

After the undocking of the Colorado, deflection observations 
were continued for three days, and variations in deflections 
with the dock unloaded, due to temperature changes, of seven- 
eighths of an inch were noted. 

The battleship Iowa was docked on June 27, 1905, for a 
record test, having a displacement of 11,600 tons at the time, 
and was carried on the dock for forty-eight hours. The speci¬ 
fications required that a 16,000-ton ship should be raised in 
four hours from the time the ship took the blocks until the 


FLOATING DRYDOCKS. 


69 


keel was out of water. For the equivalent of a 16,000-ton 
ship the dock was pumped to a freeboard of four and one-half 
feet. From the time the Iowa took the blocks until the keel 
was out of water was one hour and thirty-seven minutes; 
to the time the dock had a freeboard of four and one-half feet, 
two hours and forty-two minutes. During the docking of the 
Ioura one of the three pumping engines was out of commission 
for forty-two minutes with a slipped eccentric, so that the 
actual time of operation of the dock is about half that allowed 
by the specification. 

The Iowa was docked by uniform pumping, as in the case 
of the Colorado, and carried for forty-eight hours without 
change of water ballast in the dock. The specification required 
that when a ship had been docked by uniform pumping until 
the dock had a freeboard of two feet the deflection in the entire 
500 feet of length of the dock should not exceed three inches. 
When the dock reached a freeboard of four and a-half feet 
with the Iowa, the deflection was about two inches. During 
the first twenty-four hours, the dock remaining uniformly 
pumped, the deflection increased to four inches in the 500 feet, 
and during the second twenty-four hours showed a recovery 
to three and three-eighths inches. 

Immediately following the undocking of the Iowa* the dock 
was pumped up to the same depth of water in the compartments 
as when the ship was docked, which gave a freeboard of nine 
feet and six inches, and it was found that the dock had a hog 
of one inch. During the night this hog disappeared, and early 
the next morning was a half inch sag. I he greatest deflection 
in the bearing length of the Iozva while carried on the dock 
was about one and three-quarter inches. The deflection obser¬ 
vations indicate that there was no permanent set caused by the 
docking, and that temperature variations may cause consider¬ 
able hog or sag. 

After the undocking of the Colorado the main and docking 
keel blocks were found to be uniformly indented about one- 
sixteenth of an inch with no crushing. No change was made 
in the blocks for the Iowa, and after undocking she was found 
to have rested even more easily than the Colorado. 


70 


FLOATING DRYDOCKS 


With two feet of freeboard and one foot of water remaining 
in the pontoons the carrying capacity of the dock is 18,500 
tons, and a 20,000-ton ship could readily be docked with suffi¬ 
cient freeboard to admit of easily working on its bottom. 

The results of the docking tests with the Dewey dock show 
that it is considerably in excess of the contract requirements 
in strength, time of operation and capacity, and is in all re¬ 
spects a very noticeable advance on all floating dry docks which 
have been so far projected or built. The greatest innovation 
is the requirement of uniform pumping. This not only insures 
safety from careless or unskilled handling, but makes it possi¬ 
ble to dock nearly all ships with keel straight, or with as 
much hog or sag as circumstances may render desirable, by 
suitably distributing the water ballast in the dock. The ship 
may be also hogged or sagged while on the dock, should occa¬ 
sion arise for so doing. With thirty feet of water over four- 
foot keel blocks the side walls of the dock have a freeboard 
of eleven feet. By taking the keel blocks down to two feet 
and sinking until the side walls have a freeboard of three feet, 
forty feet of water may be had over the blocks, so that a ship 
may be taken into the dock in any condition of disablement. 

Although a heavier ship, the deflections with the Colorado 
were less than with the Iozm, on account of the much longer 
bearing length of the Colorado's keel. With the uniform 
pumping the strains caused by the Iozm were much greater 
than will be caused by any other ship in the service, projected 
or built; so that the dock has had the most severe test that can 
be imposed on it. 

The dock was constructed under the supervision of Civil 
Engineer Leonard M. Cox, U. S. N., and tested by a Board of 
naval officers, consisting of Captain Adolph Marix, senior 
member; Naval Constructor J. H. Linnard, Commander J. F. 
Parker, Commander W. F. Worthington, Naval Constructor 
J. H. Rock, Civil Engineer A. C. Cunningham and Assistant 
Civil Engineer J. S. Shultz. The Board was assisted in the 
tests by Civil Engineer Cox. 










Dewey.”—End Pontoons Seef-Docked on Center Pontoon. 




















Floating Drydock “Dewey.”—Center Pontoon Self-Docked on End Pontoons. 









































Floating Drydock “ Dewey.”-Center Pontoon Self Docked on End Pontoons. 

















FLOATING DRYDOCKS. 


71 


THE SELF-DOCKING TESTS OF THE STEEL 
FLOATING DRYDOCK FOR CAVITE, P. I.* 

By Civil Engineer Leonard M. Cox, U. S. Navy. 


In the specifications forming a part of the contract between 
the Government and the Maryland Steel Company for the con¬ 
struction of the steel floating drydock for Cavite, P. I., it is 
provided that the structure, after completion, shall be given 
a thorough working test before final acceptance. This test, 
as provided for in the contract and its specifications, comprises 
three distinct operations: The lifting, within a given time, to 
a specified freeboard and with limited deflections, of the heavi¬ 
est type of cruiser ; the lifting, under similarly specified con¬ 
ditions, of the heaviest battleship; and, finally, the lifting of 
its own hull clear of water. 

On June 10, 1905, the dock was launched from the building 
basin at the manufacturers’ works and was immediately towed 
to the mouth of the Patuxent River, the site selected for the 
official tests. After preliminary trials of the machinery, the 
dock was declared ready for testing on June 17, 1905, just one 
month before the expiration of the contract time of twenty- 
seven months from the date of award. O11 June 23d, the 
cruiser Colorado was docked, followed by the battleship Iozva 
on June 27th, and preparations were at once begun for the self¬ 
docking trials. 

An article appearing in this issue of the Journal (page 
714) fully describes the successful docking of the Colorado 
and the Iozva. This article, coming as it does from the officer 
who wrote the specifications under which the dock was con- 

* Reprinted by permission from Journal of the American Society or Na\al 
Engineers, Volume XVII, No. 3. 




72 


FLOATING DRYDOCKS. 


structed and who was closely connected with its preliminary 
design, is of peculiar interest, but, as it covers only the ship¬ 
docking tests, it may not be out of place to add a brief account 
of the subsequent self-docking operations. 

In regard to the desired self-docking qualities of the dock, 
the specifications provide that it “shall be so designed and 
arranged as to be readily self-docked without the aid of divers 
or auxiliary constructions”; that the working stress of any 
portion of the dock or its connections shall be limited to 
“15,000 pounds per square inch in self-docking, with a wind 
pressure of 30 pounds per square foot of exposed surface”; 
that “when self-docked all under-water portions shall be raised 
to a height of not less than 5 feet and shall be safely and 
readily accessible for inspection, painting and repairs”; and, 
that with the dock at light-draught line, “all self-docking and 
strain-transmitting connections shall be above water.” 


U8L£ Z 


CA»L£3 

' C * e,w 



Although plans and complete descriptions of the structure 
have already appeared in the Journal (Vol. XV, page 472) 
and other technical publications, it may help to a clearer under¬ 
standing of the operations to give, briefly, a general outline 
of the design in so far as it affects the self-docking features 
before attempting to describe the working tests. The dock is 
built in three sections. The center section, or pontoon, is 316 
feet in length, with side walls overhanging 80 feet on either 
end. Two end pontoons, each 90 feet in length, with low 
independent side walls, are attached to the center pontoon in 
such a way that the overhanging side walls of the latter are 
enclosed between the independent walls of the end pontoons 




















FLOATING DRYDOCKS. 


73 


and rest diiectly on their decks when the sections are con¬ 
nected for docking ships. There are vertical and horizontal 
connections between the pontoons, the vertical connections 
consisting of seven elements, each made up of forty-four 2-inch 
bolts; the horizontal, of four elements, one along each edge of 
the overhanging side walls, each made up of ninety-six ij4- 
inch bolts. The lower ends of the vertical connections are out 
of water at light draught. 

The self-docking is accomplished in two stages. After 
removing the connection bolts, the end pontoons are hauled 
clear of the overhanging walls of the center pontoon, turned 
so that the direction of their lengths is perpendicular to the 
axis of the dock, and brought over the deck of the center pon¬ 
toon and centered on blocking, as in the docking of ships. 
The center pontoon is then pumped to the desired freeboard 
by the main pumping engines. The second stage of the oper¬ 
ations has for its object the lifting of the center pontoon. The 
end pontoons are submerged to a depth giving twelve inches 
clearance between the blocks and the bottom of the center pon¬ 
toon at light draught, and are then drawn under either end 
and centered, after which they are pumped to the desired 
freeboard by means of a separate pumping plant installed in 
the independent side walls, to which steam is furnished by a 
flexible hose led from the forward and after boilers. 

On Saturday, July 15th, 1905, the work of arranging the 
blocks of the center pontoon for receiving the two ends was 
finished, and all vertical connection bolts, together with half 
of the horizontal bolts, were removed. On Monday, cables 1 
and 2 (see accompanying sketch), were slipped from the end 
pontoon bitts, starboard side, forward, and made fast by haw¬ 
sers to bitts on the top of the overhanging side walls. On 
Tuesday, cables 3 and 4, forward, were similarly slipped and 
belayed on the port side-wall bitts. All horizontal connections 
were removed and steel drift pins placed in the bolt holes at in¬ 
tervals of about twenty-five feet, with men standing by for each 
pin. At 12.15 P- M. the flood valves of the forward pontoon 
were opened, and ten minutes later the horizontal connection 


74 


FLOATING DRYDOCKS. 


diaphragms came gently apart. With the aid of a small tug 
boat, the end pontoon was hauled clear of the overhanging 
side walls at 12.53 P. M., and made fast against the starboard 
side of the center pontoon at 1.35 P. M. Cables 2 and 3 were 
then slipped from the tower-deck bitts and made fast to the 

forward-deck bitts of the center pontoon with two shots of 

% 

chain which had previously been detached from cables 1 and 
4. An anchor-hoy and tug was used in shifting moorings and 
handling cables. 

On July 19th, cables were slipped from the after pontoon 
bitts and made fast to the side-wall bitts as was done in the 
case of the bow pontoon. All horizontal connection bolts were 
removed and the flood valves opened at 10.20 A. M. The 
pontoon began to drift out with the tide at'10.49, an d was 
hauled to the port side of the dock and made fast at 12 M. 
Cables 2 and 3 were then slipped from the tower bitts and 
made fast to the after center pontoon bitts as for the bow 
pontoon. 

On July 20th, the center pontoon was submerged to an aver¬ 
age draught of thirty-three feet, giving a little over twelve 
inches clearance between the bottoms of end pontoons and the 
blocking for a draught of nine feet. The end pontoons were 
then hauled in and centered over the keel blocks. Pumping 
was commenced at 12.26 P. M., the blocks were awash at 
1.25, and the pumps were stopped at 1.40 with a freeboard 
of eighteen inches, the total time of pumping being one hour 
and twenty minutes. All mud valves in end pontoons were 
opened at 1.00 P. M., and the compartments drained with the 
falling water. 

During the next three days the pontoons were held on the 
blocks and the time was spent in cleaning and repainting such 
parts of their bottoms as seemed to require it, and in arrang¬ 
ing the blocking on the ends for seating the center pontoon. On 
July 24th the mud valves of the end pontoons were closed at 
8.40 A. M., the flood valves were opened at 9.15 and closed 
with the pontoons afloat at 10.00 A. M. The pontoons were 
lashed together in tandem and drawn out with the tide, being 


FLOATING DRYDOCKS. 


75 


clear of the dock at 11.31 A. M. Both pontoons were then 
made fast to the starboard side of the center pontoon. When 
floated, the end pontoons had an average draught of 4. ^9 feet, 
making their joint displacement 3,164 tons. 

The 25th of July was consumed in arranging the blocking, 
and on the 26th the work of docking the center pontoon was 
begun. Cables 2 and 3 were slipped and led by hawsers to 
side-wall bitts, the dock being held in the meanwhile by cables 
1 and 4. At 8.30 A. M. the stern pontoon was sunk to suffi¬ 
cient depth to permit its being hauled under the overhangs, 
and at 11.40 it was in position and ready for sinking to full 
draught. At 1.05 the flood valves were opened, and at 3.50 
P. M. the pontoon had reached an average draught of thirty- 
one feet, the sinking being carried on very deliberately on 
account of the possible effect of the strong ebb tide, nearly 
always to be contended with at this point. After reaching this 
depth the pontoon was drawn under the center pontoon and 
centered over the blocks. The pumps were started and con¬ 
tinued until the pontoon reached a draught of twenty-eight 
feet, and the center was firmly seated. 

On July 27th the dock was simply held in position and 
observations made for possible settlement. On July 28th the 
bow pontoon was drawn into position, sunk to a draught of 
thirty-one feet, drawn under the center pontoon and, at 2.20 
P. M., pumped to a uniform draught with the stern pontoon. 
Both end pontoons began pumping full speed at 2.20 P. M., 
and reached a freeboard of eighteen inches at 7 P. M. After 
holding the dock in this position for four days, the work of 
undocking vas commenced, but, on account of bad weather, 
this work was discontinued and the end pontoons were held 
at twenty-six feet draught until August 2d, when the stern 
pontoon was hauled from under the center and connected in 
its proper position. Two more days were lost on account of 
the weather, and the bow pontoon was withdrawn and con¬ 
nected on August 4th. No difficulty was encountered in 
entering the connection bolts, and each pontoon was sunk, 
hauled out, pumped to proper draught and connected in twelve 
hours time. 


76 


FLOATING DRYDOCKS. 


The total working time consumed in the self-docking tests, 
exclusive of the time spent on the blocks, is about fifteen days, 
and, when it is taken into consideration that this work is 
absolutely new, that it was necessary to proceed with caution 
during the first test, and that the crew was naturally unused 
to its work, it would seem probable that the time for future 
self-dockings could easily be reduced to ten or eleven work¬ 
ing days. 

Numerous devices have been exploited in the past, all claim¬ 
ing more or less novel means to enable floating docks to lift 
their own hulls for inspection and repairs. Few of these de¬ 
vices appear practical, and still fewer have been actually tried 
on large structures. The most prominent among the self¬ 
docking types is the Clark & Stanfield modification of the 
Rennie type, represented in this country by the naval docks at 
Algiers, La., and at Pensacola, Fla. The Algiers dock was 
successfully self-docked by her builders during the acceptance 
tests, and required for the operation about forty days. It suc¬ 
ceeded in lifting the pontoons to a height of four feet and the 
side walls to a height of twenty-one inches above water. The 
Pensacola dock has docked her intermediate pontoons, but is 
only now, for the first time, attempting to lift the end sections. 
So far as I am aware, the new Bermuda dock has never been 
completely docked, nor has the new naval dock at Pola. Aus¬ 
tria, the latter being an entirely new design. 

The Cavite dock has, so far, proven a complete success, and 
the self-docking features are particularly satisfactory. In the 
light of experience with other self-docking types, it would 
seem that, as regards the saving effected in time and labor, 
facility of control and simplicity of operation, the self-docking 
problem has been satisfactorily solved and the greatest objec¬ 
tion to the floating dock per sc completely eliminated. 

The self-docking tests were conducted by a Board of which . 
Captain Adolph Marix was senior member, and Naval Con¬ 
structor W. G. Du Bose and Civil Engineer Leonard M. Cox, 
members. 














































I I 





































The Start From Solomons Island. 











FLOATING DRYDOCKS. 


77 


THE VOYAGE OF THE DEWEY* 

By Lieutenant Commander F. M. Bennett, U. S. Navy. 


It was the intention of the writer to make this narrative 
simply a plain tale of the sea, describing- mishaps, accidents and 
obstacles met with and expedients resorted to by the naval ex¬ 
pedition that transferred the floating drydock Dewey from 
Chesapeake Bay to the Philippine Islands. In putting the 
numerous events and incidents of the voyage together it ap¬ 
pears that some account of the preparation and equipment of 
the expedition is necessary to save many explanations as the 
story progresses, and a few paragraphs will therefore be de¬ 
voted to the fitting out before the actual seafaring begins. 

The floating dock itself needs little description in these 
pages. It has been widely described and pictured in naval and 
technical journals and by the press at large, so it may be as¬ 
sumed that anyone sufficiently interested in the subject to read 
this article already knows what sort of structure we had to 
deal with. In a very general way, then it is only necessary 
to say that the dock is a rectangular box 500 feet long, 135 
feet wide, and 18 feet deep, with side walls 14 feet thick and 
45 feet high extending along almost the whole length of the 
longer sides. Viewed from a short distance, these high and 
narrow brown-painted side structures look remarkably like the 
breakers about the mouth of a coal mine or the grain eleva¬ 
tors in the towns of the middle West and suggest not at all 
any. form of known sea-going craft. The industrial expres¬ 
sion of the whole fabric is added to by four tall sheet-iron 
smoke pipes of the kind used on saw mills projecting from the 
tops of the side walls high into the air. 

When equipped in all respects for sea the dock s weight, or in 


* Reprinted by pefmission from The Proceedings of the United Staies Naval 
Institute, Volume XXXII, No. 4, December, 1906. 




78 


FLOATING DRYDOCKS. 


other words its displacement, was about 12,000 tons and its 
draught somewhat less than eight feet. Floating so lightly, 
more than ten feet of the main hull or pontoons extended above 
water which, with the side walls, made a sheer blank surface 
55 feet high and 500 feet long upon which the wind might 
act to our disadvantage. J11 even the lightest breeze, unless 
dead ahead, the dock would trail off to leeward far from the 
course, while a moderate or fresh breeze abeam would set it 
over thirty degrees or more and seriously interfere with its 
steady towing. Even in a calm or a head wind we found 
that it would not tow straight but would yaw at intervals from 
one side to the other as a kite does in the air. With the wind 
anywhere forward of the beam the tendency of the dock was 
to head into the wind, which was natural, as the forward end 
was restrained by the towing bridle while the after end was 
free to drift off before the wind. 

To offset to some extent the tendency of the dock to drift 
to leeward it was customary to let water into its ballast com¬ 
partments. This reduced but slightly the area exposed to 
the wind, but the most important result was in adding greatly 
to the dead weight that the wind had to push through the water. 
Without engaging in any very refined mathematical calcula¬ 
tions we found about 1,500 tons of water would sink the 
dock one foot, and 6,000 tons would increase the draught four 
feet. This method of adding to the weight and draught of 
the dock was always resorted to in high winds and heavy 
seas and was of great value in enabling it to resist both, the 
impact of the seas especially. The amount of water admitted 
varied with the weather from one to four feet, the latter being 
the prescription for a strong gale. This great addition to 
the weight of the dock of course made towing more difficult, 
but when water ballast was used the situation was generally 
such that the question of making progress on the course was 
one of secondary consideration. 

The dock was never sunk enough to bring the pontoon deck 
awash, which would have required the admission of about ten 
feet of water, or 15,000 tons, and the subsequent obligation to 


FLOATING DRYDOCKS. 


79 


pump it out. W hen the expedition was fitting - out in the 
United States various newspapers freely spread abroad infor¬ 
mation as to how the dock ought to be handled in bad weather. 
One article that I remember stated in all seriousness that in a 
gale the dock would be submerged thirty feet and the towing 
vessels would then snugly moor themselves inside, there to lie 
in comfort and quiet until fair weather! The experiment was 
not tried; in fact it was quickly learned that proximity to the 
dock, even in moderate weather, was undesirable. A little ex¬ 
perimenting was done in changing the trim of the dock so it 
would have a different draught at the ends, but no noticeable 
results followed, notwithstanding the well-known advantage 
gained in towing a log by the big (or the little?) end, so well 
established by a steerage argument of great antiquity. 

The greatest obstacle to towing that we encountered was in 
the structure of the dock itself in presenting a perfectly square 
wall-like surface to be dragged through the water and against 
head seas. Inasmuch as the law authorizing its construction 
specified that it was for use in the Philippine Islands, 12,000 
miles from where it was built, it is strange that the design was 
not influenced by the knowledge that such a long voyage would 
be the first event in its history. Similar floating docks have 
been built with V-shaped or rounded ends to facilitate towing, 
and otheis have been taken to sea provided with false bows for 
the same purpose. Had this dock been fitted with sea-going 
ends or bows I may say with absolute certainty that the voyage 
to the Philippines would have been accomplished in two months 
less time and with much less risk of losing the dock; that 
thousands of dollars worth of towing gear destroyed by hard 
service would never have been used; that many more thou¬ 
sands of dollars worth of coal would not have been burned, 
and that the officers and men of the towing squadron would 
have been spared much anxiety, physical hardship and, at 
times, actual peril. This, at least, is my belief after having 
seen the square-ended obstinate structure dragged by main 
strength, through fair weather and foul, across one hundred 
and ninety-seven degrees of the earth’s longitude. 


8o 


FLOATING DRYDOCKS. 


About the middle of October, 1905, it was decided to start 
the drydoac for the Philippines, via the Suez Canal, as soon as 
possible. A previous study of wind and weather conditions 
in different parts of the globe at different seasons of the year, 
made by officers on duty in the Navy Department, had resulted 
in the conclusion that the expedition should leave the United 
States early in December at the latest in order to have the 
best chances for good weather along the Suez route. It was 
already too late in the season by two months or more for the 
route by way of the Cape of Good Hope to be attempted, 
though it had been considered earlier. The orders eventually 
issued to the commander of the expedition did not specifically 
bind him to pursue any particular route, but directed him to 
deliver the dock to the commandant at the Cavite naval station, 
the manner of getting it there being left entirely to his good 
judgment. 

The naval supply ship Glacier and the colliers Brutus and 
Caesar were designated as the towing ships, and the work of 
fitting them for that service was taken in hand at the Boston 
and Norfolk Navy Yards. Some time later the naval tug 
Potomac was detailed for the expedition, but as she is a tug 
pure and simple little or no preparation had to be made in her 
case. The principal work on the large ships consisted in in¬ 
stalling towing machines and in removing from the after part 
of the upper decks all rails, stanchions, boat davits and other 
fittings that would interfere with the free scope of towing lines. 
On board the Glacier at the Boston Navy Yard three large 
steel arches or towing frames were erected across the after 
deck to hold the tow line up clear of the hand-steering gear 
and over two small deck houses. These arches were capped 
with solid oak timbers a foot square and as hard as bone, being 
old ship material that had been seasoning for years, but in 
use we found that the steel towing hawser in working back 
and forth would bite into them like a saw and tear out big 
chunks of the tough fiber with every lateral movement. Later, 
at the New York Navy Yard, the largest of these arches was 
reinforced with more oak covering, and two heavy king posts, 


FLOATING DRYDOCKS. 


81 


stepped on deck, were secured to it with steel bands, their 
object being to limit the athwartship travel of the tow line. 
These towing frames were very clumsy and inconvenient, and 
they were not necessary, since the Brutus and Caesar were 
made fit for their work without them. On those vessels the 
towing machines were placed higher than on the Glacier and 
the hand-steering gears were protected by timber casemates 
built over them. In consequence they had better control of 
their hawsers and a clearer space in which to handle them than 
we had on board the Glacier. 

The towing engines for all three ships were supplied by the 
American Ship Windlass Company, of Providence, Rhode 
Island, and were the largest size (designated as No. 5) that 
the makers could deliver within the limited time allowed. 
Larger ones would have had to be made especially for the 
expedition, and it is unfortunate that time did not permit such 
manufacture. The ones we had were ponderous enough to 
look at and were of the size that had proved sufficient for the 
heavy tows of barges that one sees along the Atlantic coast 
of the United States, but they were not able to hold a 12,000- 
ton dock up against the weather of the Atlantic ocean in mid¬ 
winter. When only 500 miles off shore at the start the towing 
engine on the Caesar was disabled by teeth breaking out of 
the drum gear, and three weeks later in a gale in mid-ocean 
the one on the Brutus was literally torn to pieces and the dock 
set adrift by the tow line going overboard. All three ships 
and the dock were provided with wireless telegraph outfits, 
electric searchlights and night-signalling apparatus, all three 
installations essential to the work in prospect, and the wire¬ 
less telegraph so much so that on some occasions confusion 
and possible disaster would have resulted but for the quick 
interchange of information by its means. 

The selection of low-powered steamers for such a large 
undertaking may be questioned, but when the most desirable 
requisites are considered it must appear that the ships employed 
were more suitable than high-powered cruisers or battleships 
could have been. Ability to carry coal for long periods at sea 
6 


82 


FLOATING DRYDOCKS. 


practically limited the choice to colliers, the coal problem in the 
case of the Glacier being met by putting 2,000 tons into her 
holds and refrigerator spaces. The latter vessel was selected 
of course because of her cold-storage outfit which enabled her 
to carry fresh provisions in ample quantity for all the vessels 
in the expedition. When towing under favorable conditions, 
the Glacier of 7,000 tons displacement developed from 1,700 
to 2,000 horsepower; the Caesar, of 5,000 tons, developed 
about 1,200, and the Brutus, displacing 6,600 tons, developed 
only about 1,100 horsepower. That is, the actual indicated 
horsepower of the three big steamers was only about 4,000 alto¬ 
gether, which had to be applied to keeping their own weights, 
aggregating nearly 19,000 tons, in motion before any of it 
could be felt by the dock. At a glance it would seem that' 
a single cruiser of 6,000 or 8,000 tons displacement capable 
of exerting 6,000 or 8,000 horsepower would have been better 
than all three of the towing ships combined. But aside from 
the question of prolonged coal and food supplies there are 
objections to such a rapid conclusion. 

One objection is that the inertia of the heavy masses of the 
three ships moving uniformly, though slowly, served as a pro¬ 
tection to the tow lines against sudden jerks to which they 
would have been subjected by a light high-powered cruiser in 
rough weather. Another is that there is a sufficient element 
of danger in being shackled to an object like a drydock in 
stormy, unfrequented seas to make it desirable to have more 
than one ship present. Yet another objection lies in the fact 
that at one time or another we broke nearly every unit in the 
towing outfit at least once, showing that any increase of 
power would have only added to the troubles of the expedi¬ 
tion. Any increase of speed would have been resisted in such 
a multiplying ratio by the square-fronted dock that abnormal 
power and great increase in dimensions (and cost) of towing 
gear would have been necessary to permit of any noticeable in¬ 
crease of speed. All things considered, the ships selected for 
the undertaking were as suitable as any that our navy list 
affords. The only really serious defect they had was that 


FLOATING DRYDOCKS. 


33 


they were all single-screw vessels. When it was necessary, 
as it was many times, to take the dock and each other in tow 
in rough water and high winds at sea, much time and labor 
was lost and positive danger sometimes incurred because of 
the lack of handiness of these big and clumsy single-screw 
ships. 

Commander W. F. Fullam, of the Glacier, was selected as 
commander of the expedition late in October, and that ener¬ 
getic officer went immediately to the Patuxent river, where 
the dock was moored, to see what would be necessary to 
prepare it for sea. He found that everything in the line o,f 
preparation had yet to be done. Aside from the fact that the 
dock was afloat it was as unfit for sea as a newly-finished store¬ 
house in a navy yard might be. There was not a fathom of chain 
or hawser for towing it, either on the dock or provided else¬ 
where; no working anchors, no chain cables for anchors, no 
capstan for handling anchors, no appliances for handling tow¬ 
ing lines, “no nothing,” literally. O11 the whole expanse of 
the great pontoon deck there was not a solitary ring bolt or 
link plate for stoppering chains or hooking leading blocks! 
The dock was moored with mushroom anchors at the corners, 
but there was no provision for getting them in on deck in case 
of getting underway, no hawse pipes nor billboards onto 
which' they could be hove for safe transportation. It is need¬ 
less to enumerate here all that was found lacking at this in¬ 
spection, but the thoroughness of Commander Fullam’s report 
deserves mention as well as the foresight shown by him as to 
| what would be needed on such an unusual voyage. He speci- 
) fied not only the number and size of towing hawsers required, 
but also the quantity of spun yarn that should be provided. 
In all things, great and small, the report was complete, and 
insistent in tone as to the genuine need for everything asked 
for. Among the important things asked for were, of course, 
such essentials as anchors and chains, a steam capstan, towing 
bitts, chain bridles and life boats, but such lesser items as 
coaling trucks, rigger’s tools, deck stoppers and heaving lines 
were not overlooked. 



8 4 


FLOATING DRYDOCKS. 


It had now become the first of November, and the receipt of 
this report at the Navy Department set in motion much manu¬ 
facture and preparation at widely separated points, each Bu¬ 
reau interested turning to with a will to hasten forward its 
own share of the work. The equipment shops at the Boston 
Navy Yard undertook the manufacture of a quantity of huge 
towing thimbles for 15-inch manila and 6-inch wire lines, with 
shackles, swivels and pelican hooks to go with them. Swivels 
weighing half a ton and shackles, thimbles and pelican hooks 
weighing a quarter o,f a ton each are unusual, but they were 
provided for this expedition and were none too heavy, as 
some of them were broken in use. The same Bureau from 
its Boston department provided four 9,000-pound Dunn an¬ 
chors and 480 fathoms of 2*4-inch chain for them, 360 
fathoms of 2*4-inch chain for towing bridles, a great quantity 
of manila cordage, and many other items. A fine steam cap¬ 
stan was found by taking one from the armored cruiser New 
York, then laid up for repairs at Boston. The Wall Rope 
Works undertook the manufacture of twelve 15-inch manila 
hawsers, each 1,200 feet long, and the Roebling Bridge Works 
agreed to supply four 6-inch steel hawsers, also 200 fathoms 
long. Twelve of these were required, but the Roebling firm 
could not promise that number within the short time allowed, 
and eight were ordered by cable from England. As soon as 
completed these heavy lines were sent to the New York Navy 
Yard where, under the supervision of Chief Boatswain William 
Anderson, they were fitted with the thimbles and shackles from 
Boston and otherwise prepared for use. Five of the big 15- 
inch lines were doubled by splicing the ends together and a 
towing thimble was secured in the bight at each end, the 
two parts being seized together to prevent cable-laying by 
stout lashings every two fathoms along the whole length. As 
thus made up, each one constituted a towing span weighing 
six tons, which was an ugly object to run as a tow line and 
a worse one to haul back on board ship after it had been a 
month or more in the water. The steel hawsers were fitted 
with a thimble and shackle in one end, the other end being 


< IV/BE L/H£ 














































































































































































































































































































































































■ 
































FLOATING DRYDOCKS. 


85 


left free for clamping to the drum of the towing machine; 
they weighed about 7,000 pounds each. The plate accom¬ 
panying this article shows the details of all these fittings, but 
the order in which the various parts are assembled in the draw¬ 
ing is not meant to show the actual arrangement in use. At 
the New York Navy Yard also was provided a great quantity 
of other gear for the expedition—bale fenders, chafing mats, 
hook ropes, deck tackles, snatch blocks, oil bags, chain and 
manila straps, bull ropes, cork buoys .for running messenger 
lines, etc., etc. 

The Bureau of Yards and Docks set a force of men at work 
on the dock in the Patuxent river, building chain lockers, fit¬ 
ting link plates to the deck, installing the steam capstan, fitting 
boat davits, and remedying other deficiencies. In compliance 
with an urgent recommendation of Commander Fullam a 
wooden trestlework bridge was built across one end of the 
dock to afford means for handling bridles and tow lines. There 
was a steel swinging bridge at the other end of the dock to 
which purchases could be hooked for handling the towing gear 
and other heavy weights, but it was plainly essential that both 
ends of the dock be so fitted. By keeping a bridle and towing 
span shackled together and ranged on the deck ready for use 
at the rear end of the dock much time and labor was saved 
after the dock had been adrift, as towing could be resumed 
from that end, leaving the damages at the other end to be 
repaired at leisure. Phis belated completion of the dock was 
badly handicapped by being done at an inclement season of 
the year and at a point remote from supplies, where material 
and tools had to be brought from a distance, and wheie it was 
difficult to induce workmen to remain because there was no 
place for them to live except such as could be found in a pecu¬ 
liarly forlorn and squalid village. I he result w r as that the 
work was much protracted and days w r eie lost that would 
have been worth twice their length could they have been 
used in towing the dock at sea. There were some provoking 
delays in fitting out the ships, but in the end the towing ships 
were assembled in the Patuxent equipped and leady foi work 
ten days before the dock was ready. 



86 


FLOATING DRYDOCKS. 


Something may now be said about the personnel of the 
expedition. The colliers had what are officially designated as 
‘'merchant officers and crews.” The masters, mates and en¬ 
gineers were Americans, probably above the average of the 
competent self-reliant type so usual in our merchant marine. 
The crews were Chinese, a relic of former service in the 
Asiatic fleet, and were satisfactory, the men being well-behaved, 
industrious and capable of doing their work well on deck and- 
in the firerooms. They knew no English, and therefore there 
was no one on deck at night capable of reading or sending a 
signal except the officer in charge of the watch. This was a 
very disquieting situation, for in case of accident that indi¬ 
vidual would in all likelihood have to give his time to assur¬ 
ing the safety of his own ship, without any opportunity to 
warn others by signal. As a simple matter of safety English- 
speaking quartermasters or signalmen should have been as¬ 
signed to those ships. 

The Glacier had a regular naval crew, the usual run of men 
available on the receiving ships, and not selected in any way 
for this special service. If anything, this crew was somewhat 
below the average of a man-of-war crew in morale, the ship 
having been commissioned in Boston. The original crew was 
insufficient in numbers for the work of the ship, and upon the 
urgent recommendations of the commanding officer additions 
were granted, until we finally left the United States with fifteen 
men in excess of complement. This being still inadequate, fur¬ 
ther additions were subsequently made by taking men from the 
Tacoma in the Mediterranean Sea. The seaman branch of 
this crew was sadly deficient in experience, as it was com¬ 
posed almost entirely of mere boys, just rated ordinary sea¬ 
men, enlisted only a short time, with no sea service, and no 
naval experience except at the Newport training station. They 
were willing and intelligent, but with every day devoted to 
stevedores labor there was no opportunity to teach them how 
to become handy about a ship. Their inexperience was par¬ 
ticularly trying in the matter of a life boat’s crew at sea, it 
being often necessary to communicate by boat with other ves- 


FLOATING DRYDOCKS. 


87 


sels or the dock, and in rough weather it was really perilous 
to lower a boat manned by these boys. I am aware of the 
desirability of keeping experienced men in the fighting ships, 
but in view of the service ahead of the Glacier it seems that one 
good seaman might have been taken from each of a dozen 
ships of the Atlantic fleet without impairing their efficiency 
and a capable life boat’s crew in each watch thus provided 
for us. 

The dock was manned by a composite crew, or rather by 
two crews, an arrangement not conducive to harmony or best 
endeavor. One consisted of a temporary crew shipped for the 
voyage, twenty-two men in all, including the sailing master 
and the two mates. The other nine men all told, including 
a dock master, was the permanent force of the Bureau of Con¬ 
struction and Repair, to remain with the dock after reaching 
its destination to attend to its maintenance and operation. The 
temporary crew comprised a rigger, whose services were found 
invaluable, a wireless telegraph operator, a “dock expert’’ at 
$300.00 per month, twelve seamen, cook, steward, and two 
messmen. The dock expert had been a superintendent or 
foreman with the company that built the dock, and was so 
familiar with its fittings that he was a useful person to have 
1 on board. He became dissatisfied notwithstanding his high 
{' rate of pay, and resigned when we reached Port Said. 

, Of the seamen I cannot speak with enthusiasm. They were 
of the kind referred to in sea stories as deep-water sailors 
I and appear as interesting and even heroic characters in those 
I works of fiction, but masters and mates, whose opportunities 
for knowing them excel those of the sea writers, do not hold 
them in great esteem. In the sea tales it usually appeals that 
disloyalty to employers and insubordination to officeis aie 
reckoned as virtues in the forecastle, and from what I saw and 
heard of affairs on the dock it would seem that the men weie 
average specimens of their kind and indulged then pioclivities 
with much more freedom than is permitted by a forceful ship¬ 
master. It is but just to say that at sea, well away from land, 
they did much excellent and hard work, but the shoie seemed 




88 


FLOATING DRYDOCKS. 


fatal to their energies; perhaps this is the reason why they 
are called deep-water sailors. Sailors though they were by 
trade, they were far more lubberly in boats than were the young 
ordinary seamen o,f the Glacier, and they could not compare 
in a life boat with the Chinese crews of the colliers. 

At Las Palmas, the first port where we stopped, these men 
left the dock half moored to the mole and went ashore almost 
in a body, remaining as long as they chose, behaving on shore 
in such manner as to cast discredit upon the expedition, and, 
in general, showed total disregard for the obligations they were 
under. Working parties from the towing ships had to go on 
board the dock to moor it properly and laborers from shore 
were actually hired to do the work of the crew while in that 
port. The sailing master appeared incapable of exercising any 
control over his men, and the commander of the expedition 
could not legally discipline them because they were merchant 
seamen, shipped under the navigation laws, and entitled to a 
hearing before a United States consul. Several of them 
deserted or were discharged at that port and their places filled 
by shipping new men. At that port also, authority was 
received from the Navy Department to add six seamen to the 
complement of the dock, the original allowance having been 
found insufficient. I he new men taken on were mostly natives 
(Spaniards), and the dock proceeded toward a late Spanish 
colony with a crew that might, if inspired by patriotic fanati¬ 
cism, have been disposed to scuttle it rather than see it become 
a feature of a naval station that so recently had been Spain’s. 

The work of preparing the Glacier for the expedition was 
somewhat hampered at Boston by rains and cold weather pecu¬ 
liar to the advanced season and was not completed until the 
night of December 2. She left the navy yard the next day in 
a driving storm of sleet and rain, felt her way around the 
Nantucket shoals with the sounding machine, and arrived at 
the New L ork Navy Lard the afternoon of December 5. All 
the towing gear and supplies that had been collected there were 
ready for delivery: too ready in fact, for while our small crew 
was still on the wharf making fast the mooring lines a train 


i 


h 


¥ 










Towing Ships as Seen from the 


“ Df.wey.” 


Face p. 88 



















FLOATING DRYDOCKS. 


89 


of railway cars piled high with the 15-inch manila hawsers was 
backed down alongside the ship and a message delivered to the 
effect that the hawsers must all be stowed on board before 
sunset. Y\ ith the force available we could with equal ease 
have taken down the Brooklyn bridge and stowed that in the 
hold within the same time limit. A week followed that is 
easily remembered. Railway cars, coal and provision barges, 
trucks, wagons, carts and boats, clustered about the ship with 
cordage and gear of all description, coal, frozen meat, ice, vege¬ 
tables, paymaster’s stores, everything in the way of stores and 
supplies for six months for all the vessels of the expedition. 
Hundreds of men and horses delivering the goods and a work¬ 
ing force of less than thirty on the Glacier to receive and stow 
them. As soon as the situation became known to the com¬ 
mandant large working parties were furnished from the receiv¬ 
ing ship and from the yard departments, and the work of 
loading the ship went forward rapidly, though uncomfortably 
because of the cold weather. 

Commander H. H. Hoslev reported for the command of the 
Glacier and the towing expedition December 11, Commander 
Fullam having been detached before the ship left Boston. The 
morning of December 13 we left the navy yard and proceeded 
to sea, entering the Chesapeake the following afternoon, where 
we had to anchor about 8 P. M., off Rappahannock Spit, 
because of very thick weather. Continued on up the bay the 
next morning in the face of a fierce northeast gale with rain, 
sleet and snow, arriving in the Patuxent river early in the 
afternoon. Took the Potomac alongside at once and trans¬ 
ferred the gear and stores that we had brought for her from 
New York. She had arrived only an hour before we did, and 
the Brutus and Caesar had been there since the day before. 
We saw also for the first time, dimly through the driving snow, 
the enormous bulk of the drydock, a curious looking object, 
but one that was to become very familiar before we were done 
with it. 

The next morning at daylight we went alongside the dock, a 
difficult operation in the high wind prevailing and because there 





90 


FLOATING DRYDOCKS. 


were no suitable fittings on the side of the dock for a vessel to 
make fast to. The Caesar came to our other side and we 
began transferring the great mass of material we had brought 
to both, the Brutus taking the place of the Caesar as soon as the 
latter had received all her gear. In some respects this was the 
most dangerous and uncomfortable period in the history of the 
expedition. A storm of sleet and snow had swept over the 
region just before, and as a result our gear was all wet and 
everything covered with ice and snow, making the work in 
hand unusually difficult and cruel. Many of the weights to 
be handled were very heavy, the reels of wire hawsers, for 
instance, weighing over three tons and the manila hawsers five 
tons each. Owing to the slipping of straps and tackles several 
men received minor injuries, and one officer, Boatswain Her¬ 
bert, had a leg broken and had to be detached from the expedi¬ 
tion. Another warrant officer, Boatswain Arthur Smith, was 
disabled for several days with a damaged jaw, but he was in 
luck because he very narrowly escaped being killed. The acci¬ 
dent in which he was involved was caused by the slipping of an 
icy boom topping lift around the gipsy head of a winch, letting 
the boom come down by the run and allowing a steam launch 
with its crew to drop overboard from a height above the rail. 
Chief Boatswain Phillip Mullen sustained a fractured rib dur¬ 
ing this same strenuous period. 

Within three days, one of which was Sunday, but not a day 
of rest, we had everything distributed to the different vessels 
and then had to go to work on the dock, which was found far 
from ready for sea. The crews of the Brutus and Caesar 
coaled the dock, a slow and difficult operation, requiring several 
days because of the great height to which the coal had to be 
hoisted, and the Glacier’s men were employed in moving a 
great number of keel and bilge blocks away from the ends of 
the dock and in disentangling the chain bridles from a confused 
pile and ranging them ready for use. As soon as the New 
York’s capstan was set up, the chains of the four 9,000-pound 
working anchors were stowed into the temporary chain lockers 
and the anchors pointed ready for letting go. The crew of the 


FLOATING DRYDOCKS. 


91 


dock, before described, was on board at this time but was not 
at all conspicuous in these busy scenes. Our men did much 
hard and excellent work at this time amid very uncomfortable 
surroundings, and it seemed a pity that we had to do> this 
heavy work at such an inclement season, when the dock had 
been there idle all through the pleasant autumn months. 

The question of what lights should be carried by the flotilla 
naturally received consideration while other preparations were 
going forward. Commander Hosley came to this duty from 
the position of supervisor of the harbor of New York, and 
as such was in touch with the seafaring element of that port, 
from which, notably the Pilots’ Association, he received con¬ 
siderable valuable advice. The seamanship experts at the 
Naval Academy contributed some more, and he, of course, 
discussed the matter with the masters of the colliers, who were 
most directly interested in precautions that would reduce the 
chances of collision. The decision arrived at after considering 
all this counsel was the following, issued as a general order to 
the squadron under date of December 22. 

“When engaged in towing at night, the leading vessel will 
show the three white towing lights and the side lights required 
by law. All the other vessels including the Dewey will show 
the red lights (two) required by law for a vessel not under 
control, as well as the side lights required by law. During the 
day the proper shapes as laid down by law must be shown. All 
vessels will carry a white light aft so screened as not to be 
visible forward of the beam, to assist the others in steering. 
The Dezvey must also carry such a light. 

“Vessels will at all times keep the spar decks well lighted 
as a ‘show’ to passing vessels ; cargo lights at both ends are 
suggested when practicable.” 

Further thought led to the conclusion that the lights above 
specified were not certain of giving passing vessels the correct 
information as to the nature of our formation, and on the 
principle that the more lights shown without actually violating 
the law the safer we would be, the order was modified as fol¬ 
lows the day that we went to sea. 






92 


FLOATING DRYDOCKS. 


“When engaging in towing, all steam vessels will carry the 
three vertical white mast-head lights and side lights; the Dewey 
will carry side lights and no mast-head lights. All vessels will 
carry a white light aft so screened as not to be visible forward 
of either beam. The day shapes will not be carried unless 
especially ordered.” 

Later, at sea, when it was observed that the Dewey was very 
dark and that lights at her ends appeared disconnected as 
though on different vessels a considerable distance apart, she 
was directed to show several white lights along each side. Car¬ 
rying lights as prescribed in the modified order, there was 
never any confusion or danger of collision, mariners of all 
nations being active to give us a wide berth. 

The colliers and the dock not being allowed the general 
signal book of the Navy, we had to use the international code 
for all ordinary communication and for the routine reports, 
such as sick, coal on hand and expended, latitude and longitude, 
etc. The one-flag signals of the international code for use 
between vessels towing and being towed were found not appli¬ 
cable to our situation, and Commander Hosley prepared and 
put into use a special one-flag series of about twenty important 
signals. These were easily memorized by most of the officers 
having to use them and were very simple and convenient. Some 
of these, like I—“all right, go ahead,” or J—“go ahead, full 
speed,” were regarded with pleasure; others excited a contrary 
emotion because they meant trouble: V was particularly hate¬ 
ful, signifying “the hawser has carried away.” Z meant “man 
overboard,” the same as it does in the regular international 
code, but fortunately none of us ever had occasion to hoist it. 
A few special two-flag signals were used to supplement the one- 
flag series. The flags used were all international letters, but a 
few navy-code flags were used for special purposes, the tele¬ 
graph flag, for instance, being used as an order for the wireless 
operators to stand by for a message. The international code 
contains five pennants, just enough to provide distinguishing 
pennants for the vessels of the squadron—C for Caesar, D 
Dewey, F Glacier, E Brutus and G Potomac. C and D were 


FLOATING DRYDOCKS. 


93 


also used in their regular code significations as yes and no. At 
night letters and numerals were made from the navy code, 
all the vessels having been supplied with signal cards giving 
the wig-wag, semaphore and ardois systems of signalling. At 
the beginning it was sometimes difficult to communicate as 
quickly as we wished, but the officers of all the ships soon be¬ 
came sufficiently proficient for our purposes, though never to a 
degree that would have made them feel comfortable in the 
battleship fleet. 

December 26 the work of unmooring the dock was begun, 
an operation that consumed all that day and the greater part 
of the next. Preliminary to heaving up the mushroom moor¬ 
ing anchors the dock was anchored with 9,000-pound Dunn 
anchors, one at each end. Billboards, or more properly hawse 
pipes, had been fitted for the mushroom anchors at one end 
of the dock and the anchors were hove up into them by means 
of long deck tackles leading to the New York’s capstan located 
in the center of the pontoon deck. At the other end the bill¬ 
boards were not completed, and never were, as the material 
for them was subsequently used at sea for strengthening plates 
to keep the dock from coming apart. It was therefore a more 
difficult job to get the anchors up at that end and landed on 
deck, but this was simplified greatly by the able seamanship 
of Captain Hutchinson of the Caesar. He noticed that the 
chains were of a size that would fit the wildcats of his steam 
capstan, volunteered his services, and brought the Caesar , bows 
on, up to that end of the dock, keeping her thus underway for 
several hours in a tideway and giving an exhibition of ship 
mastery that could not well be excelled. We on the dock 
unbitted the chains one at a time and gave him the bitter ends 
by means of a tail rope previously passed through the Caesai s 
hawse pipe. They then hove the anchor up with their steam 
capstan, and when it came up to the bow, considerably higher 
than the deck of the dock, we got hold of it with tackles, and 
by hauling in while they eased out the chain fiom the Caesai 
successfully landed it. All four anchoi s at that end of the 
dock were picked up in that way, not without tiouble, foi they 


94 


FLOATING DRYDOCKS. 


had been so carelessly dropped after the self-docking tests of 
the dock that we found two of them, from opposite corners, 
foul of each other and very hard to get clear. 

The forenoon of December 28 was consumed in running 
the towing lines from the dock to the Brutus and Caesar, those 
two vessels being anchored in column at suitable intervals 
ahead of the dock. The so-called “bow” of the dock—the end 
upon which was the swinging bridge—was pointed up stream, 
which made it necessary to turn completely around after getting- 
underway, to aid in which evolution the Potomac was put on 
ahead of the Caesar. Each collier had one of the 200-fathom 
6-inch hawsers upon the drum of her towing machine, the 
hawser being shackled into a double 15-inch manila span; one 
of these was between the Caesar and the Brutus, and two, 
shackled end to end, were in the interval between the Brutus 
and the bridle on the dock. While getting underway and 
working out of the river the greater part of the wire lines were 
kept reeled up on the drums of the towing machines, but were 
nearly all paid out as soon as open water was reached. These 
practical details may appear trivial to the readers of the Naval 
Institute and may be thought more in place in a “First Mate’s 
Manual,” but if there is ever another expedition of the kind the 
people engaged in it will be grateful for anything in print relat¬ 
ing to the small but important details of this one. Little prac¬ 
tical matters like these unquestionably pertain to the naval 
profession, even if not military, and should not be beneath the 
consideration of naval officers. When the expedition was fit¬ 
ting out, the suggestion reached me from two or three sources, 
all naval, that the service assigned was rather unprofessional 
and even demeaning. It is not my task, for obvious reasons, 
to offer any plea for seamanship in the Navy, but I think I 
may ask without presumption, in the present commendable 
enthusiasm about target practice and gunnery, if many officers 
are not forgetting that common seamanship is still a profes¬ 
sional requisite? 

Everything being ready, the colliers and the dock hove up 
their anchors and at 2.30 P. M., December 28, the long journey 


FLOATING DRYDOCKS. 


95 


began without a delay or hitch of any kind. The small collier 
Lebanon■, from which we had been coaling when we had noth¬ 
ing else to do, and the tug Mohawk were put alongside the 
dock on the inshore side while getting underway to aid in 
turning it around and to prevent any tendency to swing into 
shoal water. The Potomac let go when well pointed out of the ' 
river, leaving the two colliers towing. The start was disap¬ 
pointing, for the night came on thick with much rain and 
many squalls from almost dead ahead, making the navigation 
of the bay difficult and keeping the speed down to less than 
three knots. The weather was better in the morning, and the 
Potomac resumed towing ahead of the Caesar , increasing the 
rate of progress to between three and four knots; this was 
still disappointing, as there was a general impression commu¬ 
nicated to us from naval discussion that we ought to make 
at least five knots per hour. At 10.30 that evening we passed 
out at the capes of the Chesapeake and into the Atlantic ocean, 
where numerous adventures and novel experiences awaited us. 

December 31 marked the first whole day from noon to noon 
that we were at sea and the day’s run was 111 miles; this was 
encouraging and led us to hope that the five-knot prophets 
might not be so far wrong after all: a hope that was doomed 
to be blasted, for in the event we did not equal that day’s run 
until nearly three months later, when, with the aid of the 
surface current that sweeps through the Stiait of Gibi altar, 
we made 115 miles the day that we entered the Mediterranean 
Sea. December 31 was distinguished in our annals for more 
things than good speed. It was Sunday, and the fust com¬ 
fortable day we had known for many weeks; we were in the 
gulf stream, with warm air and water about us, and the men in 
clean white working clothes, all in great contrast to the cold, 
dirt, and incessant hard labor that had been our portion for 
more than two months at the Boston and New York Navy 
Yards and in the Patuxent river. Besides being the last day 
of the year the day also came near being the last one of the 
drydock expedition, as I shall now attempt to 1 elate. 

Various methods of towing had been discussed before the 


96 


FLOATING DRYDOCKS. 


expedition started and all agreed that it would make too long 
and cumbersome a tow to put all four of the towing vessels 
in tandem ahead of the dock, besides subjecting the tow line 
nearest the dock to great strain. An arrangement like that 
shown by Fig. i had been proposed and was considered worth 



trying, as it would distribute the strain on the tow lines and, 
apparently, would tend to keep the dock straight in cross winds 
and seas. The Brutus and Caesar were to tow in tandem 
ahead and the Glacier and Potomac, with shorter lines, were 
to tow from the forward corners. To give this scheme a trial 
the Glacier steamed up to the dock from astern and passed 
slowly along the starboard side of it to throw a heaving line 
aboard. The Potomac at the time was towing ahead of the 
Caesar and the flotilla was making about 4jA knots on a course 
S.E. 54 S. The sea was smooth but there was considerable 
swell, and just at that time there was very little wind—light 
airs to light breezes at the most, from south. 

At a speed slightly greater than that of the dock the Glacier 
passed at a distance of 40 or 50 feet, a heaving line was thrown 
across and with it a stout messenger line was hauled over, with 
which to get the end of the wire-towing hawser on board the 
dock. Then, when the stern of the Glacier was almost abreast 
of the starboard forward corner of the dock, that unwieldy 
craft began one of its kite-like swings to starboard. Seeing 
the distance closing in, Commander Hosley, on the bridge of 
the Glacier, put the helm to starboard to sheer the stern away 
from the* dock, at the same time ringing up full speed ahead 
on the engine-room telegraph. The dock’s movement was, 
however, too sudden and unexpected to be avoided, and her 
corner hit us twice far aft on the quarter; first lightly, and 
then, on the next swell, heavily, dishing inward a considerable 
area of plating to a depth of about six inches, breaking one 









FLOATING DRYDOCKS. 


97 


frame, starting open a seam, and shattering several square feet 
of marble panelling with which the ward-room messroom was 
finished. The damage was about twelve feet above the water 
line and was in itself of no importance, but the immediate 
result of the impact brought us face to face with a genuine 
peril. The blow forced the stern of the Glacier over to star¬ 
board, the starboard helm assisting, and the ship became 
pointed diagonally across the interval immediately in front 
of the dock. It was a critical situation, affording no time for 
reflection but demanding instant action. To have tried to turn 
clear in that limited space with a port helm would almost cer¬ 
tainly have resulted in fouling the Glacier’s screw with the tow- 
lines. Without hesitation Commander Hosley went ahead 
with starboard helm, and we actually passed over the tow lines 
without accident, the ship’s stern crossing certainly less than 
one hundred feet ahead of the on-coming dock. The clipper 
form of the Glacier’s bow enabled her to ride down the line 
and force it underneath when she met it. It is not pleasant to 
conjecture what would have happened had the line caught on 
her bow and stopped her, but it is safe to say that the least 
result would have been damages to the dock and the Glacier 
that would have compelled the return of the expedition to port. 

Another perilous adventure was in store for us that same 
day. After the crew's dinner hour we took a position on the 
starboard bow of the dock as nearly ahead as we dared go 
without getting too close to the tow lines, and floated a mes¬ 
senger line to her by means of buoys. I his took considei able 
time, as the lines fouled the sharp overhanging corners of the 
dock after being grappled and had to be run several times. 
About 5 P. M. we got the end of our 6-inch steel tow line on 
board the dock and shackled into a pelican hook secured at the 
starboard forward corner. After beginning to tow we un¬ 
reeled about 150 fathoms of this line, making our position about 
half the distance between the dock and the Brutus. Oui line, 
leading off the port quarter, tended to drag the stern of the 
ship in that direction and obliged us to carry considei able 
starboard helm to keep on the course. 

7 


98 


FLOATING DRYDOCKS 


In the meanwhile the weather had become threatening, with 
rising wind from S.S.W., falling barometer, and fierce rain 
squalls, the consequence no doubt of our being then on the east¬ 
ern edge of the gulf stream. About 6.30 P. M. the ship failed 
to respond to a full starboard helm and reserve engine speed 
and came up until the wind caught her on the port bow, when 
she fell off rapidly, unable to help herself, and was soon being 
dragged stern foremost by the dock: a very awkward predica¬ 
ment for a 7,000-ton ship. Figure 2 will give a better idea of 



the situation than can be obtained from any description. A 
furious rain squall of gale force (7 to 8) was blowing at the 
time and the lights on the dock were seen so dimly through the 
driving rain that we could not tell how close we were being 
drawn toward collision. Full pressure of steam in the cylin¬ 
ders of the towing engine failed to hold the strain of the 
tow line, which veered out by bounds and with an appalling 
sound as the compressed steam forced open the cylinder relief 
valves, while the deck, heavily supported and reinforced as it 
was under the towing engine, fairly jumped with each attack 
upon it. The two large king posts previously mentioned as 
having been put in at New York were both whipped out and 
thrown overboard by the tow line, and half the top of one of 
the towing frames went with them. It was a miracle that no 
one was killed by these heavy timbers when they were flying 
b° l I the deck, ^^.lto^ethei it was a decidedly bad quarter of 
an hour. 

Commander Hosley tried his utmost to regain control of the 
ship, but in the high wind blowing it could not be done, and. as 
we could not see clearly whether we would foul the dock or 
not, he gave the order to let go our line. We unclamped it 









FLOATING DRYDOCKS. 


99 


from the drum of the towing machine and let it run overboard, 
it going with such spitefulness that its marks are still on the 
ship. It was subsequently hauled on board the dock, and we 
got it a day or two later after another memorable struggle 
with refractory forces, and reeled it back again upon our tow¬ 
ing drum. The wind veered suddenly to N.W. early in the 
first watch, blew with gale force for two hours, and then sub¬ 
sided to a moderate breeze from the same quarter. The Glacier 
never attempted that method of towing again, but on two or 
three occasions afterward, when it was fairly smooth, the 

i 

Potomac was put on one corner of the dock for short periods 
and contributed something to the general progress. Through¬ 
out the serious incident just described the other vessels con¬ 
tinued towing ahead, prevented by the rain and darkness from 
knowing that we were having trouble, and we learned from 
them later that they knew nothing of it beyond the fact that 
we had cast off from the tow. 

The next three days were comparatively peaceful; the wind, 
usually light, veered gradually from N.W. to north and N.E. 
and thus on around until it was about S.E., or ahead, by 
noon of January 3. The runs for those three days were 79, 98 
and 101 miles; still disappointing, as we had not yet had 
enough experience to realize what a huge task we had ahead 
of us. Valuable experience was close at hand and arrived the 
following day, with the wind in the southeast quadrant at first, 
gradually increasing and veering until by 1 P. M. it had 
reached the force of a moderate gale from S.S.W. and raised 
such a sea that any progress in towing was impossible. The 
Potomac had cast off at 8 A. M. to go to Bermuda for coal and 
to take the mail, and we had much difficulty and some danger 
in getting the mail on board her, so rapidly did the sea make. 
The colliers left attached to the dock took the most comfortable 
position, which was about head to sea, and steamed only fast 
enough to check the drifting of the dock to leeward. Even 
under such conditions the strain on the towing gear was great, 
and at 3 P. M. the Caesar’s towing engine was disabled by sev¬ 
eral teeth being torn out of the drum gear and the engine shaft 


■> > 
> ) ) 


IOO 


FLOATING DRYDOCKS. 


being lifted out of its bearings. They succeeded in bitting the 
wire hawser and so held on. Some studs were subsequently 
put into the drum gear in place of the broken teeth and the 
machine thus made fit to use for reeling in slack wire, but the 
Caesar always towed thereafter with her line bitted, the acci¬ 
dent having proved that towing machines of this size cannot 
manage 12,000-ton drydocks in gales of wind. 

The day’s run from noon January 4 to noon the 5th was 21 
miles, which served as a damper upon preconceived estimates of 
what we were going to do> and furnished something definite 
upon which to calculate for the future. The wind continued 
all day January 5 in the S.W. quadrant, of force 4 to 6, with 
moderate sea, the tow facing the weather. The Glacier took 
position ahead and distributed oil on the water, but so far as 
we could see there was no change in the seas that broke over the 
bows of the colliers and upon the deck of the dock. The morn¬ 
ing of January 6 the wind fell to a gentle breeze and veered 
around to N.W. Captain Hutchinson of the Caesar suggested 
by wireless that advantage be taken of this wind to get as far 
south as the 30th parallel, where he thought we would be less 
liable to have bad weather; this being approved, the two colliers 
started off to the S.E. towing the dock with wind nearly astern 
and orders to go to Lat. 30 N., Long. 65 W. At the same time 
we in the Glacier started for Bermuda to pick up the Potomac . 
This separation was necessary because the Potomac had been 
ordered to find us on the 32d parallel, and, as she had no wire¬ 
less outfit, the only way to inform her of the change of route 
was to go after her. We met her when she came out of port 
the next morning, and that evening we both rejoined the 
squadron. 

The following day, January 8, the Glacier began towing 
ahead of the Caesar, the great increase in power thus put on 
making it necessary to stop for a short time to permit the 
Brutus to bitt her wire line, her towing machine not being able 
to withstand the increased strain. The Potomac was taken in 
tow astern of the dock, which thereafter became the usual 
arrangement while crossing the Atlantic. The Potomac kept 


c 


t 


FLOATING DRYDOCKS. 


IOI 


steam enough to take care of herself, and when the weather 
made her too uneasy in tow she would cast off and keep along 
with the flotilla under easy steam. She cast off frequently also 
to aid in distributing provisions or for other services. In the 
protracted bad weather that we had a little later the Potomac 
certainly had a hard time, and life on board her must have been 
almost intolerable. There were times when it did not seem 
possible that a vessel so small could preserve herself, but she 
always came out right side up and without much damage. 

The Glacier towed at first with one of the single 15-inch 
manila hawsers, 200 fathoms long, shackled to the 6-inch wire 
from her towing machine. About 170 fathoms of the wire 
hawser would be unreeled, making the tow line about 360 
fathoms long with a dead weight of two-thirds of a ton near 
its middle where the thimbles and shackles came together. The 
plain end of the manila hawser was taken over the Caesar’s 
bow and bitted on her forecastle. This was a clumsy arrange¬ 
ment because of the amount of work necessary on the Caesar 



Fig. 3. 
























102 


FLOATING DRYDOCKS. 


after they got the end of the hawser on board. They had to 
get enough of it to take to the bitts, which was no light task, 
as a line of that size is not an easy thing to haul out of the 
water, and they had to hold it up with the cat fall while par¬ 
celling could be put omthe part that would lie in the bow chock. 
In a seaway with the ships going ahead,, and particularly be¬ 
cause the Glacier is very hard to keep under control at low 
speed, this operation was always attended with great risk of 
the Caesar losing the line after they had got the end on board 
and before it was bitted. The first step toward improvement 
was for us on the Glacier to find out how much end the Caesar 
needed (about 9 fathoms) and to put the parcelling on before 
running the line. The messenger line, a whole coil of 5-inch 
or 6-inch manila, and sometimes two bent together, was hitched 
to the hawser just below the parcelling and stopped along at 
intervals to the end. This messenger was rove through a 
snatch block on the Caesar s anchor davit, and when it brought 
the end of the hawser up to the block they had only to cut the 
stops one by one as they arrived and pass the big end, thus liber¬ 
ated, along to the bitts, ceasing to heave in of course when the 
parcelling came up over the bow chock. The heaving in of 
such a heavy line, it may be added, required the use of the 
steam capstan on the forecastle backed by a winch on the well 
deck. 

This resulted in the saving of some time and nervous distress, 
but still had the great drawback that it was necessary to cut the 
15-inch hawser forward of the bitts when it had to be let go in 
a hurry, and it was so cut four times before we had opportunity 
to prepare another improvement. This began by splicing an 
eye in the end of the hawser, well protected by parcelling, 
serving and leathering, and putting therein one of the large 
shackles figured on the plate, so it could be shackled instead of 
bitted on the Caesar. This passed through three or four stages 
of development and finally reached the arrangement shown by 
Fig- 3> which was so satisfactory that we did not try to improve 
it. With this it was only a matter of a few seconds after the 
end of the short chain came up over the Caesar's bow before 


FLOATING DRYDOCKS. 


103 


the pelican hook would be slipped into place and the welcome 
international letter Y—“hawser is fast v —would be run up. 
This put an end to the long and anxious minutes of dread lest 
the messenger carry away while holding the big hawser up 
against the pitching and wallowing of both ships, and certainly 
added much to the peace of mind of the chief officer of the 
Caesar and myself, who were both strenuously engaged when 
tow lines were being run. 

The Brutus always used a'chain bridle over her bow dipped 
through a shackle in the end of the manila span from the 
Caesar , and never had any trouble with it for the simple reason 
that the towing train between the Brutus and Caesar never car¬ 
ried away. The same elements parted at one time or another 
in all other parts of the train, so it may be considered merely as 
luck that no break ever occurred in the space mentioned. 

From January 8 to January 12 we proceeded eastward, mak¬ 
ing enough southing to reach the 28th parallel on the latter 
date, that having now been decided upon as the proper latitude 
for the crossing. The wind, not exceeding 4 in force at any 
time, was forward of the beam or ahead practically all the time, 
and the sea was only rough enough to give the ships a moderate 
sea motion. We made 388 miles during the foui days, with 
which we were satisfied. The 12th the wind freshened and 
the sea became so much heavier that even with racks our mess 
table could not be set and meals had to be taken, picnic fashion, 
wedged somewhere into a corner. 1 he colliers and the dock 
were very unsteady and the Glacier was much woise, establish¬ 
ing beyond dispute, I think, her claim as the champion roller 
of the world. The little Potomac presented a spectacle of 
abject misery, though not without an element of the pictui 
esque, as she struggled with the tall seas. Rain added to the 
discomforts of the day. About half past ten that night the 
Brutus burned the odious letter V—“hawser is carried away 
and the dock was adrift, the 6-inch wire hawser from the 
Brutus’ towing machine being the one that had paited. The 
dock began drifting to leeward, about N.YV., and we all stood 
by her, working on our lines to get ready to connect up the 

tow again. 



104 


FLOATING DRYDOCKS. 


The dock had the most work to do, as the heavy chain bridle 
with two of the 15-inch manila spans and about 100 fathoms of 
the 6-inch wire attached to it had to be hauled in, but all this 
heavy work was done and the lines ready for running again 
before noon the next day. The Brutus, Captain Hendricks, 
did remarkably quick work, getting the drum clear of the 
broken hawser and a new one reeled on in time to report ready 
at 1.50 A. M., a little more than three hours after the accident 
had occurred. On the Glacier we had the Caesar let go our 
line and discovered that it was a big undertaking, working 
with all hands in the darkness and rain, to get twelve hundred 
feet of water-soaked 15-inch hawser back on board the ship. 
We were hampered greatly by lack of deck room on which to 
work, our deck being much obstructed by ventilators and deck 
houses, and the towing frames put on at Boston were provok- 
ingly in the way. We had to haul this line in many times 
during the cruise, and with experience came to adopt a number 
of makeshifts and expedients that finally brought the operation 
down almost to the system of an established drill, but it never 
became an easy task. I shall resist the temptation to describe 
the troubles we had and how they were overcome, but I will 
say that one of our most baffling difficulties was caused 
by the malignant and almost animate manner in which the 
big hawser would cable-lay itself as the bights were hauled 
in on deck. The Caesar avoided trouble with her line by keep¬ 
ing the Brutus in tow, but this made the work more difficult 
when it came time to get hold of the dock again. 

About 1 P. M. of the day following the break the Caesar 
towed the Brutus as close to the dock as was prudent and the 
Potomac succeeded in carrying across a messenger line with 
which an end of one of the 15-inch double manila spans was 
hauled over and shackled into the end of the new wire line 
on the Brutus' drum. This took longer than it takes to write 
it, as the sea was still heavy, the dock drifted faster than the 
vessels, and the weight of the gear to be handled was about 
up to the limit of the facilities for holding it, so it was 4 P. 
M. before the two colliers began towing on a course again. 


FLOATING DRYDOCKS. 


105 


An incident of this accident was damage to the stern rail of 
the Brutus that cost more than $2,000 to repair at the first 
port we stopped at. The next morning the Glacier went ahead 
of the Caesar, ran her lines, and began towing again, the 
Potomac being taken in tow astern of the dock. Everything 
proceeded satisfactorily until 4 A. M., January 17th, when 
“without warning,” as the newspaper writers say, the Glacier's 
15-inch line parted where it passed through the bow chock of 
the Caesar. This was the simplest accident that could occur r 
as it left two ships fast to the dock, and so little was off the 
end of our line that we did not have to get a new one ready. 
After heaving in our lines and getting them ready to run again 
we took the Potomac in tow with an 8-inch manila line, the 
weather indications being such that it did not seem advisable 
to shackle into the main tow at that time. 

The next morning, January 18th, we all stopped for a short 
time while funeral services were conducted on board the Caesar 
over the remains of a Chinese seaman who had died the night 
before of beri-beri. Then we proceeded; the Glacier shackled 
in ahead of the Caesar and the Potomac took her place in 
tow astern of the dock. In running lines to the Caesar we 
floated them with buoys in every instance but one, when the 
weather permitted the use of a boat. The buoy method is very 
simple and easy as described in the seamanship books, and a 
midshipman can write it out nicely on the blackboard and get 
a 4 for it any time. In real life, however, on the high seas, it 
is difficult. With a stiff breeze blowing across the course or 
on the bow, as almost always was the case with us, and a good 
sea running, it was difficult to keep as clumsy a ship as the 
Glacier parallel to the course of the colliers or at the same 
speed that they were advancing, which made the game of 
catching the buoy a rather engaging one for the Caesar. The 
Glacier was about six feet lighter forward than aft, which 
caused her to fall off rapidly if stopped or run at dead slow 
with the wind on either bow and greatly increased the difficulty 
of keeping her in place long enough to run the lines. Even 
after the Caesar got the end of the messenger line to her cap- 


io6 


FLOATING DRYDOCKS. 


stan there yet remained ample trouble for us, for two hundred 
fathoms of wet 15-inch line is about as difficult to get over¬ 
board safely as it is to get back again, and we always had a 
violent time with jammed check stoppers, foul slip ropes, and 
innocent ordinary seamen who seldom failed to step inside 
each bight of the hawser as it started to run. When one of 
these events was over the deck looked as though a battle had 
been fought on it, strewn as it would be with stranded cordage, 
splintered woodwork and broken tools. Under very adverse 
weather conditions it took us once four hours to get hold of 
the Caesar, but an hour was usually sufficient time and on two 
or three occasions the whole operation was completed within 
fifteen minutes after streaming the buoy. 

Following January 18th for nearly a week came the most 
comfortable and successful period in the transatlantic voyage. 
The wind was mainly in the northeast quadrant and light, 
and the sea was smooth except for a swell that kept the ships 
all rolling more or less. Going east along the 28th parallel 
as closely as possible we made 612 miles in six days, and might 
have made several miles more had we not stopped two 
or three times to issue provisions and transfer stores. There 
was a funeral also, another of the Caesar's men having died. 
The satisfaction of this period was increased by our getting 
into touch with the world through the armored cruiser Mary¬ 
land, the easternmost of a chain of ships that had been deployed 
into the Atlantic for wireless telegraph tests. She telegraphed 
us the more important items of news of the world and our 
navy news, which was very welcome. After leaving the United 
States we had kept in communication with the wireless station 
on Cape Hatteras for three weeks and until nearly 1,400 
nautical miles distant, but as that is a commercial station in 
business for money no news had been given us more important 
than the telegraph operator’s comments on the weather. 

January 24th saw the end of our good weather and the begin¬ 
ning of a hard-luck period that lasted nearly a month and 
destroyed every hope of making the voyage within a reason¬ 
able time. The wind had veered slowly the preceding day and 


FLOATING DRYDOCKS. 


IO7 

reached S.E. the 24th, blowing fresh with frequent squalls of 
heavy rain varying from moderate to strong-gale force (7 to 
9 by the Beaufort scale). A rough sea resulted, and between 
wind and sea we had to abandon the idea of making any prog¬ 
ress, but faced the weather and steamed enough to keep steer¬ 
age way. The Potomac had to cast off from astern of the 
dock and take care of herself. The next day the weather was 
worse and troubles began. About 10 A. M. the Glacier lost 
steerage way, though making all the revolutions possible, and 
fell off to leeward into the trough of the sea. From this posi¬ 
tion she could not recover, her light bow preventing her from 
coming up, while the effect of her struggles dragged the 



Caesar off also, and put a dangerous strain on the tow lines. 
Fig. 4 will give an idea of the situation at that time. About 
1 P. M. the Brutus gave warning that the tow lines were in 
danger, and the Glacier therefore gave up the attempt to get 
back head to wind and had the Caesar cast her off. We had 
a wild time getting that line on board in the gale and tem¬ 
pestuous sea, so heavy that water came on board over the stern 
while we were working there. 

When free from our strain on her bow the Caesar got pointed 
head to wind by the rather simple expedient of requiring the 
Brutus to stop steaming ahead, when the dock, acting as a 
drag, hauled the collier stern foremost until the Caesar was 


io8 


FLOATING DRYDOCKS. 


straightened out, both colliers then going ahead for steerage 
way. But the dock was too big and heavy an object for them 
to hold long against such weather, and about 6 P. M. the Bru¬ 
tus signalled that her hawser had parted, supplementing the 
message soon afterward with these disagreeable particulars: 
“Towing machine a total wreck; wire went by the board and 
carried away close to hole where rove through drum. Clamp 
still remains on drum, and about forty fathoms of wire left.’ 
Released from restraint, the dock started back toward the coast 
of the United States at a speed rather better than we had 
averaged in towing it in the opposite direction, and accom¬ 
plished something more than one hundred miles of the return 
voyage before we again got it under control. In the dark and 
stormy night it was impossible to do more than stand by the 
dock, steaming slowly along with it and turning around occa¬ 
sionally when getting too far ahead. Those turns will be re¬ 
membered by all who participated in them, for it seemed some¬ 
times that the Glacier would roll completely over. As on the 
occasion of a former breakdown, the Caesar kept the Brutus 
in tow. 

The next day the weather continued so bad as to forbid 
any attempt to get near the dock and we had to watch it drift 
away, unable to even try to prevent it. The barometer this day 
was unsteady, about 30.00, fluctuating a few hundredths above 
and below that mark. More than a week before it had begun 
falling slowly, from 30.29 on January 19th until it reached its 
lowest point, 29.70, the afternoon of the 23d, when the bad 
weather was just beginning, rising thereafter slowly through¬ 
out the period of storm. It was a sure-enough case of “long 
foretold, long last.” The 27th the weather had improved to 
some extent, but there was still a boisterous sea. The wind 
had decreased to a moderate breeze and moved around to about 
S.S.W., which changed the drift of the dock to the eastward 
of north. The Potomac about noon got near enough the dock 
to run a messenger line for hauling over a towing span, but 
she could not hold the dock from drifting and was dragg'ed 
by it slowly to leeward stern foremost. This situation endured 


FLOATING DRYDOCKS. 


IO9 


the whole afternoon, the Caesar towing the Brutus clockwise 
around the dock several times and passing close to windward 
of the Potomac each time in an effort to get a line from her, 
but the Potomac drifted out of reach each time. The Glacier 
eventually sent a whale boat, though it was not a good time 
for a small boat to be abroad, and on the next round trip 0|f 
the colliers this boat, commanded by Chief Boatswain James 
Dowling, carried a line from the Potomac to the Brutus, which 
enabled the latter vessel to get the end of a towing span on 
board and secured to a 2-inch chain bridle over her stern. It 
was after 7 P. M. before everything was fast and the two 
colliers began towing the dock to the eastward. The Glacier 
towed the Potomac for the night. 

The following morning we took the Potomac alongside the 
Glacier, it being absolutely necessary that she have coal, and 
gave her 37 tons before the parting of the lines between us 
made us stop. There was considerable sea and she rose and 
fell fully twenty feet alongside us, destroying big bale fenders, 
badly damaging her side, and violently removing all our chutes 
and guards on that side, but it was a case where eggs had to be 
broken or there would be no omelette. That night, or more 
exactly at 12.30 the next morning, the chain bridle at the stern 
of the Brutus parted and the dock was adrift again beyond the 
reach of all profanity. The colliers cast off from each other 
this time, having had enough of the scheme of towing one 
another, and the day was employed in getting towing gear 
ready to run again and in hoping for better weather, the state 
of the sea that day precluding any attempt to get hold of the 
dock. Next morning the Brutus unaided got hold of the dock 
and held it up in the wind while the Caesar ran her lines from 
ahead of the Brutus. As before remarked, this kind of work 
does not proceed as smoothly in the open sea as it does in 
the text books, and it was 2 P. M. before the colliers started 
off to the eastward with the dock. The rough track chart 
shown by Fig. 5 indicates the wanderings of the dock during 
the period just described. 

The dock was taken in tow this time from what we called its 


I IO 


FLOATING DRYDOCKS. 


stern end, where a bridle shackled to a double 15-inch manila 
span had been kept ready for use ever since the expedition 
started. By the former accidents the dock had acquired two 
long pieces of 6-inch wire hawsers from the Brutus and these 
had been spliced together, making one line about 250 fathoms 



long with a thimble in each end. One end of this long line 
was shackled to the manila span just referred to and the other 
end was hauled aboard the Brutus and shackled to a new 6-inch 
wire line; the inboard end of the latter was bitted on the Brutus, 
as her towing machine was out of commission, the bitts being 


































FLOATING DRYDOCKS. 


I I I 


backed to the mainmast by chain cables. All these tow lines 
made a very long drift between the Brutus and the dock— 
about 540 fathoms, or more than half a mile—but it was an 
effective one and did not carry away. The whole tow as made 
up this time was a mile and a half long from the bow of the 
Glacier to the stern of the Potomac; as ordinarily composed it 
was only little more than a mile in length. 

The Glacier towed the Potomac that night, but the next 
morning took her place ahead of the Caesar , the Potomac mak¬ 
ing fast astern of the dock, and the procession resumed its way 
to the eastward. The wind was from N.E. east and S.E., of 
force about 4, with many rain squalls, and the sea was heavy 
enough to make us all uncomfortable, the Glacier especially 
so*, as we were then engaged in hoisting coal out of the holds 
and transferring it to the bunkers. Not a pleasant occupation 
in the best of weather, but when rolling so that the hoists of 
coal would swing viciously more than the width of the ship it 
became slow, difficult and dangerous work. The weather con¬ 
ditions, adverse as they were, soon became worse, and by Feb¬ 
ruary 4 we were again in a S.E. gale—logged as a whole gale 
at one time—with a sea to correspond. For four consecutive 
days, the big ships toiling ahead on the tow line like oxen, our 
day’s runs were 30 miles, 18 miles, minus 24 miles, and 22 
miles, or 46 miles made good in 96 hours. The night of Feb¬ 
ruary 4 the Glacier fell off into the trough of the sea in exactly 
the same manner as had happened once before, and we had 
to let go and haul in our lines, shackling in again ahead of the 
Caesar the morning of the 6th. In the weather then prevailing 
both these operations involved more toil and anxiety than can 
be understood from reading of them. From February 6th to 
the 9th the wind was not so violent, blowing with force 4 to 5 
from east, or dead ahead, most of the time, and in those days 
we advanced 47, 42 and 46 miles respectively. Another 
Chinaman was buried from the Caesar the 7th. 

Meanwhile we were watching the steady approach of a trou¬ 
ble that could not be avoided. The Potomac, though being 
towed and exercising economy, was burning about six tons of 


I 12 


FLOATING DRYDOCKS. 


coal a clay and bringing* nearer and nearer the time when she 
would not have enough on board to carry her through another 
gale. Nothing perhaps during the whole history of the expe¬ 
dition gave Commander Hosley more anxiety than did this coal 
problem of the Potomac. We hoped for moderate weather 
that would allow us to take her alongside, but it did not come, 
and her noon report February 8, only 22 tons on board, gave 
warning that no more waiting would be safe and that some¬ 
thing must be done. At daylight the next morning we left the 
tow, hauled our lines on board, took the Potomac alongside, 
and began putting coal upon her after deck, using cargo slings 
that landed 1,500 pounds at a time. The sea was heavy and 
it was wild work and did not last long, as her pitching parted 
a 4-inch wire bow-line to which she was riding, and so much 
damage to our side and herself was being done that we had to 
let her go, but not until we had poured 15 tons of coal upon 
her deck. We took her in tow with a 4-inch wire line and 
spent all the rest of that day trying to rig a trolley transferrer 
to her, but found it impracticable owing to the pitching of the 
two vessels, that of the Potomac being extreme. The next day 
we got an under-water hauling line into' operation, and with 
two days of hard work transferred about eleven tons to her, 
hardy enough to keep her alive, but enough to postpone the 
day when she would be helpless. We then devoted a Sunday 
to rigging a substantial derrick, reeving off heavy lines that 
could handle several bags at a time, and otherwise improving 
our appliances, so that between dawn and dark the next day 
22 tons were hauled over to her under water, besides a quantity 
of frozen meat and other provisions, for it appeared that 
famine “shrieked” in the Potomac's pantry as well as in her 
coal bunkers. 

The sea became less rough the next day and we called her 
alongside and dumped 43 tons upon her in short order, shoving 
her off with more than 80 tons on board altogether. Towed 
her that night, and the next morning resumed our place at the 
head of the tow, having been diverted just six days by the 
^exigency of the Potomac. In those six days the colliers had 


FLOATING DRYDOCKS. 


“3 

towed the dock 303 miles to the eastward, edging also grad¬ 
ually northward in the vain hope of getting out of the limits of 
the wind that so persistently opposed us. They sometimes 
passed out of sight of us ahead while we were working on the 
coal problem, but we closed up with them each night, towing 
the Potomac. In towing her, after parting one or two 8-inch 
manila lines, we found the best way was to give her about 80 
fathoms of 4-inch wire to which she shackled a bower chain and 
veered out 60 or 75 fathoms. The weight of the chain gave 
sufficient drop to the tow line to make it yield easily to the deep 
pitching of the ships, and we had no more trouble with it. 

Another serious matter was causing anxiety at this time. 
The rough seas that we had encountered had worked loose a 
great many rivets in the joints on the dock where the different 
sections were fastened together, and a condition had been 
reached where it was doubtful if that structure could hold 
together through another gale. It would take too much space 
to describe the details of construction that were defective, and 
I shall have to be content with the statement that the angle 
bars and rivets of which the junctions were formed were not 
heavy enough to withstand the strains that motion in a seaway 
put upon them, though they were amply strong for a fixed steel 
structure on shore. By using material left on board from 
unfinished work, some temporary strengthening plates were 
bolted up, but it was decided advisable to seek the nearest port 
where permanent repairs could be effected. This decision was 
the more positive because we had been so long at sea that the 
coal and water supply on the dock was getting very low. No 
condensers had been provided for the steam machinery on the 
dock, and as the many accidents had caused that machinery to 
be used a great deal, tens of thousands of gallons of fresh water 
had been blown into the air in the form of exhaust steam. 
After our experiences with the Potomac we were not disposed 
to try to give either coal or water to the dock in a seaway. 

Being thus compelled to seek “any port in a storm,” we 
headed for Las Palmas in the Canaries, carrying our adverse 
winds with us until actually within the lee of that group of 
8 


FLOATING DRYDOCKS. 


114 

islands. The Potomac was detached February 17, when about 
400 miles from port, and sent on ahead with despatches and 
with the dock expert, who was to make arrangements for the 
necessary repairs. The rest of us plodded on. dragging our 
incubus behind us, and the morning of February 21 arrived off 
the south side of Teneriffe. where we stopped and spent the 
day, letting go and hauling in towing lines and running others 
suitable for towing into port. The Brutus, with no towing 
machine to use, could not heave in her lines, they being far 
beyond the capacity of winches, and the whole long train of 
lines from her had to be hauled on board the dock, the Brutus 
then being out of action, as the damages she had sustained 
disqualified her for towing. The Caesar had secured to the 
other end of the dock with the wire line from her towing drum 
and the Glacier ran her same line to the Caesar's bow. The 
two ships then proceeded with the dock in tow, but the (to us) 
short scopes of tow lines gave us no confidence, and the fol¬ 
lowing morning we stopped and put in a hundred-fathom dou¬ 
ble manila span between the Caesars line and the dock. At 
noon the next day, February 23, we stopped off Las Palmas 
and the dock hove in this span, the Glacier cutting out of the 
tow at the same time. A light breeze was setting in shore, 
drifting the dock toward it, and there was a very anxious time 
for an hour or two while this work was in progress. The span 
was at last gotten in and the wire line secured, when the 
Caesar, now entirely alone, got the dock pointed and towed it 
about two miles to the port of La Luz, passing safely through 
the narrow opening between the breakwaters and landing it 
alongside the east mole as skilfully as a steam launch should 
bring a cutter alongside. We were just 57 days from the 
Patuxent river. 

We were three weeks at that port having repairs made on the 
dock that would easily have been accomplished in the United 
States in half the time and at much less cost, but we were in 
contact with a breed of men that cannot be hurried and that has 
all its enterprise in promise for to-morrow. About 6,000 rivets 
were renewed, new angle bars fitted and heavier ones sub- 


FLOATING DRYDOCKS. 


US 

stituted for the old ones, so that when all was completed the 
dock was more seaworthy than when it left the United States. 
YY e hastened this work much by making up a working party 
of twenty mechanics from our ships, who worked seven hours 
each night under the direction of the ships' engineers and 
accomplished a very fair proportion of all the work done. The 
delay was availed of to repair the damages that the Potomac 
and Brutus had sustained, to obtain coal and water, and to buy 
a quantity of cordage, for, notwithstanding the very liberal 
supply we were fitted cut with, the vicissitudes of the Atlantic 
voyage had destroyed almost everything we had from 8-inch 
manila hawsers down to small stuff. We also got there from 
the United States, brought by the U. S. S. Tacoma from 
Naples, three complete drum gears and other spare parts for 
the towing machines, and were thus enabled to put those 
machines into good working order again. We were indebted 
to the wireless telegraph for these spare parts, for when the 
Caesar’s machine was disabled, January 4, we had telegraphed 
an order for repairs through the U. S. S. West Virginia, then 
in Hampton Roads about 500 miles distant from us, and a few 
days later we repeated the order to the Texas, off Charleston, 
whose call we had accidentally picked up. 

The afternoon of March 17 the dock was taken to sea by the 
Brutus towing ahead, the Potomac alongside, and the Caesar 
stern-to astern with quarter lines run so she could use them to 
steer the dock clear of the shipping and the mole heads. It 
was a very difficult operation, but they got outside safely and 
the two colliers were towing toward Gibraltar before dark. 
The Potomac went with them and began towing ahead of the 
Caesar the next morning. The Glacier had to remain behind 
to settle the bills, which were advantageous for the inhabitants 
of the port, that for coal alone being more than $30,000. 
Shortly after noon the next day the Glacier left port and re¬ 
joined her command at ten o’clock that evening. O11 this trip 
of 700 miles from Las Palmas to the Strait of Gibraltar we 
found, as we had in crossing the Atlantic, that sailing direc¬ 
tions and pilot charts are not infallible; only in this case the 


FLOATING DRYDOCKS. 


I 16 

failures were in our favor. A northeast (head) wind and con¬ 
trary current were so certain for this region and time of year 
that we expected 50 miles a day to be a good average for the 
run. It was a pleasant surprise, therefore, to find light airs 
or light breezes only for several days and a smooth sea, except 
for a long westerly swell; the latter made us roll abominably 
but did not interfere seriously with progress, the colliers and 
the Potomac keeping up an average of about four knots all the 
time. 

March 23 the Potomac was sent on ahead with despatches 
and mail to Gibraltar, the Glacier taking her place at the head 
of the towing column. In letting go the Potomac's line on the 
Caesar it struck a Chinese seaman and broke his leg in two 
places besides injuring him badly about the head. The ships 
were rolling deeply, but we sent a life boat with the surgeon to 
attend him, sending the boat to bring him back later in the day. 
Both trips were made successfully, but the boat was consid¬ 
erably damaged in hoisting the second time, being stove against 
a large mooring shackle in the ship’s side located exactly be¬ 
tween the li|fe-boat davits and near the water’s edge. We 
always used a jackstay and lizard in lowering and hoisting 
boats in rough weather and much damage was thus prevented, 
but the device could not save the boat from the badly located 
mooring shackle just as it came out of water. Oil was used 
frequently on these occasions, but I am sorry to say that I 
never could see the slightest benefit resulting from it. A 
ship’s boat is such a small object in a heavy sea that it is 
bound to be thrown about pretty roughly, oil or no oil. 

Early the morning of March 25, little more than a week 
from Las Palmas, we passed in at the Strait of Gibraltar, and 
that day broke our record, making 115 miles for the day’s run, 
thanks to the surface current through the strait. Our wel¬ 
come into the Mediterranean was not cordial. Soon after pass¬ 
ing Tarifa we met an easterly wind with much rain and the 
behavior of the barometer gave us great concern. That instru¬ 
ment had been falling slowly from 29.90 the day before and 
now began to go down at an almost alarming rate, reaching 



FLOATING DRYDOCKS. 


I 17 

29.31 at 8 P. M. Having become somewhat attentive to 
weather signs during our experience in the Atlantic, we were 
much interested in this phenomenon, and I was myself com¬ 
pletely deceived, not believing such a low pressure could be 
relieved without a gale, and figuring to myself the loss of the 
dock should it break adrift in such narrow waters. But noth¬ 
ing happened : the wind, never stronger than a moderate breeze, 
veered around rapidly during the night to south, S.W. and 
west, the rain ceased, and when morning broke we were bowl¬ 
ing along with a fine breeze astern and everything lovely 
except the barometer, which was still below 29.40. It appeared 
later that the barometer is not an oracle in those seas, for we 
had fair winds and bright skies for the next four days and 
broke our record once more, making 119 miles. 

March 30 our luck changed. We had then advanced far 
enough to the eastward to open out that wide reach of the 
Mediterranean from the south of France to Algeria between 
the Balearic Islands and Sardinia, and there we fell in with a 
cold north wind and heavy sea, causing the ships to roll and 
labor heavily and putting great strain on the tow lines. The 
Glacier finally had to let go, leaving the two colliers to hold 
the dock up against the seas and take chances on the tow lines 
surviving. The lee shore, the coast of Algeria, was only about 
sixty miles away, but the situation was not serious, as the 
wind did not increase and the sea was not making, being an 
old one. It subsided the next day and had almost disappeared 
by dark, long before which time the Glacier had shackled in 
ahead of the Caesar and we were all towing under favorable 
conditions to the eastward again. Four fine days followed, 
during which we made 450 miles and established a new record, 
having made 124 miles one day south of Sicily, where an 
easterly current helped us twelve or fifteen miles at least. 

Passing from the Malta Channel into the eastern basin of the 
Mediterranean we met a moderate breeze from almost ahead 
that gradually freshened during the following days, through 
the various stages of breezes and gales, until after five days it 
attained the force of 10. The successive days runs indicate 


118 


FLOATING DRYDOCKS. 


the gradual development of this discouraging opposition—107 
miles, 77, 52, 24, minus 40, and minus 52, the dock being adrift 
the last day. April 7, the day that we made 24 miles, the tow 
lines began to complain, and about 3 P. M. the Glacier let go 
and hauled in her lines, which was difficult work. The colliers 
continued to face the weather, but the dock took them steadily 
to leeward, as shown by the track chart, Fig. 6. The next day, 



K‘l ^ 

_ i 

NooH bill 

_q$ (etW 


\ 

Ta.m. 

"•-sir 

\ooti 

b f4oo H 7 ft 


8 <t T 

\ 



m 

floor 

r IlhR 


flooH 

lo1£ 


—~— °-- 

Sa.m.lWv 

3 - 


/G°F. 


n°a. 


iVB.Long. 


35 " M 


Fig. 6. 


April 8, moderate to fresh gales prevailed, with squalls of 
whole-gale force (10), and a sea heavier and more disturbing 
than any that we saw in the Atlantic ocean. Just before noon 
the dock broke adrift and began scudding rapidly to leeward, 
broadside to in the trough of the sea and rolling and pitching 
more deeply than we had ever seen it do before. The break 
occurred in a big triangular shackle joining the legs of the 
dock’s bridle to the first towing span, but as all parts of the 
shackle were lost, we never knew what part of it failed. The 
colliers cast off from each other and hauled in their lines, which 
in that weather was a laborious and difficult undertaking, the 
accomplishment of which before dark spoke eloquently of the 
energy and resolution of their officers. 

Idle ships without steaming did not drift as rapidly as the 
dock, while in steaming as slowly as possible before the sea 
they would go too fast. This made it necessary to run before 
the sea and bow it alternately, and compelled us several times 















FLOATING DRYDOCKS. 


119 

to pass through the ordeal that seamen dread—the turning of a 
steamer across a heavy sea in a gale. The usual precautions 
were taken about covering hatches and securing movable arti¬ 
cles, and oil was used freely with noticeably good results. The 
books say that before attempting to turn in such a situation 
you must wait for a lull in the storm, but my observation on 
this occasion and on similar ones in the Atlantic is that lulls 
are not frequent enough nor of sufficient duration to be worth 
considering. The Glacier was pooped several times when run¬ 
ning before the sea, but that was almost wholly stopped by a 
very liberal use of oil from the well deck forward. A barrel 
was lashed in each water-way over a scupper and the oil 
allowed to run through a faucet in a very small stream, which 
was found a much more convenient and certain method than 
the use of bags. The colliers, being lower and heavier in the 
water, behaved better in this storm than the Glacier did, though 
they probably took more water on board, or clean over them, 
when making the turns. The Potomac weathered the gale 
without great distress, but she certainly presented a spectacle 
that was almost tragic. 

This day, the most disheartening of the whole voyage, was 
cheered to some extent by friendly voices coming to us through 
the storm. About the time that the dock broke adrift our 
wireless office caught the call of the U. S. S. Brooklyn, then 
about 200 miles to the eastward of us, bound westward from 
Alexandria. W e told her our troubles and received kind offeis 
of assistance from her and also a promise to find us and stand 
by until the weather changed. Our messages were overheard 
by the British cruiser Sutlej, 100 miles or more away, and she 
also proposed to come to our assistance. As that vessel was 
homeward bound from the China station and probably in a 
hurry to get to England, it was very kind and seamanlike in her 
to offer to delay her voyage because of our misfortune. Light¬ 
ning that evening stopped wireless telegraphy and we could 
not give these ships our position, in consequence of which we 
did not see the Sutlej at all and the Brooklyn did not find us 
until four o’clock the next afternoon. 


120 


FLOATING DRYDOCKS. 


An interesting and noteworthy incident of this storm was 
the presence on and about the ships of thousands of land birds, 
varying in size from large cranes, hawks and owls to small 
finches, swallows and thrushes, many of them of very beautiful 
colors and marking. Their necessities for food and water were 
such that they were almost tame, and gave us excellent oppor¬ 
tunities for observing them at close range. I suppose that 
they were migrating from their winter quarters in tropical 
Africa to the summer breeding grounds in Europe and were 
caught in the gale at sea and overpowered. A few remained 
with us until we sighted land, but the most proceeded on their 
journey as soon as the wind abated. During the same time 
there were no sea birds about, which confirms the popular 
notion that such birds are sufficiently weather-wise to seek the 
shore when a storm is brewing. 

The morning of April 9 found the situation somewhat im¬ 
proved; the wind had backed to N.E. and N.N.E. and 
decreased to force 5 to 7, making a cross-surface sea on top 
of the old sea, which was still heavy and awkward for ships 
to maneuver in. Nevertheless, the Brutus and Potomac un¬ 
dertook to get hold of the dock and actually did so, the Brutus 
having the regular towing lines hauled across and shackled 
ready for use by 11 A. M. This was the most difficult and 
dangerous piece of seamanship accomplished during the cruise, 
and was greatly to the credit of the two vessels that did it. 
The Brutus was unable to tow the dock alone in the prevailing 
sea, but she controlled its drifting enough to direct the course 
about S.S.E. and thus made something to the good. (See 
track chart, Fig. 6.) The Brooklyn arrived on the scene about 
5 P. M. and the Tacoma, from the westward, an hour later, 
we having been in wireless communication with both vessels 
all day. It appeared that the Tacoma had been cruising about 
the Mediterranean for some time looking for us, and I believe 
her executive officer is prepared to furnish statistics relative to 
coal and energy expended and distances annihilated in that 
quest. Having found us, she remained in company until we 
entered the canal at Port Said, and we were very glad to 


FLOATING DRYDOCKS. 


I 2 I 


have her with us. The Brooklyn left us at 11 A. M., the ioth, 
and proceeded on her cruise. The sea was much less rough 
that morning, and at 7 A. M. the Caesar ran her lines and 
began towing ahead of the Brutus, the two ships taking the 
dock to the eastward at about three knots speed. 

As soon as the Brooklyn left us the Glacier shackled in ahead 
of the Caesar, but in working up to the full speed we parted 
the 15-inch manila hawser forming the span between our 
wire line and the bow of the Caesar. The work of hauling this 
in, getting it out of the way, and getting another line out of the 
hold ready to run employed us several hours, lasting well into 
the night, during which time the Potomac was put into our 
place to tow ahead of the Caesar. In the morning she let go 
and the Glacier resumed her place at the head of the column, 
having put into use a new double 15-inch manila span. By 
that time all traces of the gale had disappeared; the sea was 
nearly smooth and the wind, from north, was only a light to 
gentle breeze. Under such favorable conditions we were mak¬ 
ing about 4^4 knots to the eastward and there was not even a 
remote prospect of any breakdown, when at 5.30 P. M. the 
double 15-inch manila span between the Brutus and the dock 
parted, and the dock was adrift for the fifth time. Compared 
to all the other occasions this was easy, with smooth sea and 
no wind to speak of, but it involved several hours' work haul¬ 
ing in lines and ranging them for running out again, and on 
the Brutus they had to get up a new span and prepare it for use 
in place of the one that had carried away. All this consumed 
time, and it was nearly 2 A. M. before we were all shackled 
together and towing again. The Potomac distinguished her¬ 
self on this occasion by towing the dock alone four or five miles 
to the good while the other ships were working on their lines. 
The Tacoma contributed to the common welfare also by fur¬ 
nishing a boat to run lines when the tow was being made up. 

Smooth seas and fine weather followed for five days, during 
which we made a little more than one hundred miles a day, 
none of the ships towing at full power because our towing 
gear was beginning to look very disreputable from long use 


122 


FLOATING DRYDOCKS. 


and we were afraid of it. At sunset April 18 we all anchored 
in six fathoms, three miles off the breakwater at Port Said, 
thirty-two days from Las Palmas. The next morning the 
Caesar and a canal company’s tug towed the dock in to the 
Ismail basin at Port Said and the other ships followed in soon 
after. Officials of the canal company had boarded us before 
we anchored the evening before and said they were all ready 
to start the dock into the canal the next morning, which was 
certainly a pleasant surprise for us. They found, however, 
that the dock was drawing nearly eight feet, which prohibited 
it from going through until a considerable amount of dredging 
had been done. It appeared that the central office of the canal 
in Paris had been informed several months before by our Navy 
Department that the draught of the dock was six feet, and on 
that information they had widened two of the garcs or sidings 
in the canal for places in which the dock could be tied up to 
avoid stopping traffic. Perhaps the dock did draw six feet 
when it was considered finished, but after being equipped for 
sea with anchors, chains, coal, water, provisions, men and 
stores of all kinds on board its draught was about 7 feet 8 
inches, and could not be made much less. The mistake cost 
us five days’ time, which we mourned more than any time we 
had lost through bad weather, because it could have been 
avoided and because time was now precious just before the 
expected break of the southwest monsoon. 

While waiting for the dredging to be done we had more 
than enough time to get coal and provisions, re-distribute the 
towing gear, buy some more cordage, and make all prepara¬ 
tions for the next stage of the voyage. The natives there gave 
our young seamen a valuable object lesson in coaling ship, 
which was to be expected at a port that handles over a million 
tons of coal a year and has made a record of 600 tons an 
hour—ten tons a minute—put into passing mail steamers. 
When all was done, the towing ships entered the canal, the 
Brutus on April 24 and the Glacier and Caesar the 25th, all 
anchoring in Suez Bay to wait for the dock. Commander 
Hosley returned to Port Said to take charge of the dock, and 


FLOATING DRYDOCKS. 


I2 3 


the Glacier furnished eighteen men to go through the canal 
with it and satisfy the canal company’s rule requiring vessels 
in transit to have adequate crews. We expected one or more 
of our ships to do the towing in the canal, but because they 
did not have twin screws the authorities would not permit 
them to try it. A canal company’s tug, named the Titan, of 
3,000 horsepower and twin screws, did most of the towing, 
assisted by a smaller tug ahead of her and the Potomac astern 
of the dock to push, and to keep the stern of the dock from 
yawing into the banks. She performed this difficult task so 
well as to excite the admiration of the canal officials. 

The dock entered the canal the morning of April 27 and 
arrived at Suez at 6 P. M. May 1, having made the transit 
in less time and with less difficulty than had been expected. 
The chief trouble they had was because of a beam wind of con¬ 
siderable force when the dock was moored in the siding at 
Kilometer 54. The siding was on the weather side of the 
canal, which made it hard work and destructive to mooring 
lines to get into it and harder yet to stay there. Hawsers 
parted and had to be replaced, and the mooring bollards along 
the bank, though well anchored, began coming home, making 
it finally necessary to veer all lines and let the dock take 
the ground easily on the opposite bank. This effectually 
blocked the canal and stopped all traffic for several hours before 
the wind permitted the dock to be moved. They anchored one 
night in Lake Timseh at Ismailia and the next night in the 
southern end of the Great Bitter Lake, being out of the way of 
passing vessels both nights. The trip from the latter point to 
Suez, 25 miles, was made in one day, arriving vessels being 
held at Suez that day to keep the canal clear. The canal offi¬ 
cials were very attentive and courteous, the superintendent or 
director of each division going with the dock while in his part 
of the canal, and they detailed their best pilots. I hey were 
much elated at having put the dock through safely and so 
quickly, but said frankly that they hoped no more such things 
were coming that way. The dock was actually under way only 
35 hours while in transit, or about double the time it takes a 
steamer to make the passage. 


124 


FLOATING DRYDOCKS. 




4 — J) ewe»j 

< — 13 t i cl I e, x C AcifV 

*— /OS' jms, ' cfianx 


^— \%0 -jVns* % steel wire. 


B'Rl/TUS 


^ 100 jms. dLou bfz. I s" maul fa sf> an 


<— /SO f ms. T stee.{ wire. 


C/)BS^K 


x 


<— 100 -[ms. ctoubfe 15 mamfcv S^>aw 




4r— 170 ^ ms. steef wire. 


<—GUCIER 


Fig. 7. 

















FLOATING DRYDOCKS. 


125 


In making up the tow at Suez we proceeded to “load for 
bear,” using much heavier gear than formerly. From Las 
Palmas Commander Hosley had cabled home asking that 8-inch 
wire hawsers be ordered from England, and we got them at 
Port Said; three 8-inch flexible wire lines each 200 fathoms 
long and looking almost too good to use. One each was reeled 
up on the towing machines of the Brutus and Caesar, the 
drums of which fortunately were just big enough to take them, 
and the third one was reserved as a spare. The bitts on the 
colliers had to be enlarged to suit these larger hawsers, which 
was effected quite simply by putting a shell of boiler iron, 
about four feet in diameter, over the bitts and filling the in¬ 
closed space with cement. The dock had been originally sup¬ 
plied with 360 fathoms of 2^-inch chain cable for bridles, 
enough for two bridles at each end, one to use and the other 
kept bitted in place ready to use. Seven shots, or 105 fathoms, 
of this chain were now shackled into the legs of the bridle as 
a span in place of the double 15-inch manila spans previously 
used, one of the big double shackles shown by the plate being 
used to join this span to the bridle legs. The weight of this 
chain span was about fifteen tons and of the part of the bridle 
over the edge of the dock about five tons. The 8-inch wiie line 
from the Brutus was shackled into the end of this chain span 
and the Caesar put in a new double 15-inch manila span be¬ 
tween her 8-inch wire and the bridle on the bow of the Brutus. 
The Glacier put a new 6-inch wire line on her towing engine, 
with a new double 15-inch manila span joined to it and secured 
on the bow of the Caesar in the manner shown by Fig. 3. The 
whole train, made up as described, is outlined by Fig. 7. 

A delay occurred in getting underway at Suez May 3 from a 
peculiar cause. The Brutus ran her 8-inch wire to the dock, 
where it was shackled into the chain span just desci ibed, and 
then went ahead, the dock heaving up her anchor, which 
was at the opposite end, at the same time. No amount of pull¬ 
ing was able to start the dock, and the natural supposition was 
that the heavy chain and bridle, overboard in less than fi\e 
fathoms of water, had fouled something on the bottom or had 


126 


FLOATING DRYDOCKS. 


settled into the mud deep enough to form an effective anchor. 
The Potomac was pushing behind the dock and the Caesar was 
eventually put on ahead of the Brutus, but with no result except 
some broken lines. Finally, after four hours of such fruitless 
endeavor, it was discovered on the dock that their anchor had 
picked up a big mooring chain which was holding them very 
securely! It was soon cleared and the expedition started on its 
voyage, but it was after dark before the Glacier got her boats 
and working party on board from the dock and was thereby 
delayed from getting into the tow until daylight the next morn¬ 
ing. As soon as the dock was well underway the Potomac 
parted company to return to the United States; without much 
regret, I imagine, as her small size had converted the hardships 
of the voyage into genuine suffering for her crew. 

Though something less than half the distance from Chesa¬ 
peake Bay to the Philippines had now been accomplished, a 
point is reached in this narrative from which the remainder 
may be quickly told, and will be no longer a succession of tales 
of storm and breakdowns. With full confidence in the new 
train of towing gear, the three ships steamed ahead at full 
power and got results that would have been surprising in mid- 
Atlantic. Though for the most part calm and hot—bad 
weather for steaming—the run of 1,200 miles through the Red 
Sea was made in eleven days and the same rate was main¬ 
tained through the Gulf of Aden, where we experienced both 
favorable and adverse currents, making 123 miles one day and 
97 another, though making the same revolutions of the engines 
both days in smooth water. We passed the eastern end of 
Socotra May 21, about twenty miles south of us, and entered 
the open ocean, where no monsoon was found; only a swell 
and light breezes from S.S.E. and south, and, after we had 
advanced about 200 miles, occasional passing showers with 
light variable winds. Sighted Minicoy June 1 when we were 
passing through the eight-degree channel. 

It is within the observation of the oldest inhabitants about 
Bombay that the southwest monsoon very rarely sets in during 
a period of moonlit nights. It was full moon this year on 


FLOATING DRYDOCKS. 


I27 


the sixth of June, the night our expedition was passing Point 
de Galle, and the monsoon had not yet broken, nor did it 
break until the moon quartered, a week later, and considerably 
later than the annual average time. Lecky, than whom there 
is no better authority, ridicules the idea that the moon has influ¬ 
ence over the weather, but nevertheless the southwest monsoon 
broke in the Indian Ocean in 1906 about two weeks later than 
usual, and if the full-moon period at that time did not delay it, 
what did ? That two weeks’ respite was the making, or rather 
the mending, of our fortunes in the towing squadron. From 
Ceylon to the north end of Sumatra there is a pronounced 
easterly current, and with that and fine towing weather com¬ 
bined to help us we broke all previous records several days 
in succession, and one day, June 9, we reached our high-water 
mark with 152 miles. Very early the morning of June 13 
violent rain squalls, with fresh to strong breezes, fell upon 
us from S.S.W., raising a heavy sea and throwing the ships 
into more uncomfortable motion than we had felt for two 
months. This was probably the overdue ‘‘burst” of the mon¬ 
soon, but we were so nearly beyond its reach that we did not 
care whether it was or not. The next day we passed Pulo 
Bras and into smooth water behind Sumatra in the Strait of 
Malacca, where good weather favored us again. 

Just after midnight the morning of June 21 we arrived off 
the port of Singapore and felt quite proud of ourselves, for we 
had hauled the refractory dock 5,000 miles in forty-eight days 
without a breakdown and with only a few brief delays. These 
were occasioned by one funeral, a Chinese seaman having died 
on the Brutus , and by the necessity of slowing down about once 
a week to allow boats to visit the Glacier for fresh provisions 
and ice. A leaking joint in the feed pipe of the Glacier obliged 
her to stop for about two hours, which stopped the whole 
flotilla, as she was towing at the head of the column. A 
similar accident on the Caesar did not compel us to stop, as 
she stopped her engines and the other ships kept on at full 
speed, carrying the Caesar along like a dead locomotive in 
the middle of a freight train. In the course of the forty-eight 


128 


FLOATING DRYDOCKS 


days the Glacier was out of the towing line fifty-two hours, 
having gone into Colombo for coal and to exchange mails. 

In entering port at Singapore two accidents occurred that 
had no serious results, but each came close to being a disaster. 
It so happened that we arrived there at the change of the 
moon, with its accompanying spring tide and darkness, and 
the hour of our arrival was unfortunately such that we struck 
an unusually strong tide running with us close to the port. 
We rounded Raffles light shortly before midnight of an ex¬ 
tremely dark night and the next hour the flotilla made nine 
miles, half of which was due to the tide, but this was not a-s 
welcome help, as the immediate problem was to stop and not 
to make speed. According to previous practice the Glacier 
cast off and sheered out of the column to heave in her lines. 
Soon afterward the Caesar slowed down to reel in some of 
her wire hawser and immediately things began to happen. The 
Brutus closed up on the Caesar so quickly that she had to stop 
and back, and the dock, driven onward by the powerful tidal 
current, swept up dangerously close to the Brutus. In this 
situation, which was surely a critical one, both colliers went 
ahead at good speed, the Caesar to escape from the Brutus 
and the latter to get away from the huge mass of the dock 
looming up in the darkness astern. When they got opened out 
they found the dock adrift, the big double shackle between the 
chain span and the dock’s bridle having carried away when the 
lines came taut. 

I believe all this happened because the people on the colliers 
did not realize in the darkness how strong the tide was running 
and therefore did not think of the possibility of the dock having 
a progressive movement of its own. Nothing in our previous 
experience with it suggested anything but a sudden stop when¬ 
ever the towing force was removed. At any rate, they were 
all fortunate to get out of it without a serious smash-up, for 
the results of six months of hard sea-faring came near to 
being marred there within as many minutes. The water was 
about 50 fathoms deep where this occurred: the dock was 
therefore allowed to drift along with the tide until it got into 


FLOATING DRYDOCKS. 


I29 


about 25 fathoms, when it was brought up with two of the 
4,000-pouncl mushroom anchors on the end of 180 fathoms 
of 6-inch wire line, the Glacier and Caesar standing by. The 
break, occurring where it did, left the Brutus with fifteen tons 
of chain overboard on the end of her wire tow line, and this she 
could not heave over the rail with all the power of her winches. 
I11 such predicament she steamed into the port dragging the 
long and heavy chain over the bottom, and stopped when she 
got to a good place without being obliged to anchor, the chain 
over her stern attending to that. Later, when the dock had 
arrived and anchored, the Brutus dragged the chain into prox¬ 
imity, when it was unshackled, and the end taken to the dock 
by an 8-inch manila line, after which it was an easy matter 
to get it on board with the powerful steam capstan of the 
New York. 

Heaving in the 180 fathoms of wire with two anchors on it 
proved a hard task for the dock, and it was almost 9 A. M. 
before that structure was underway again, being in tow of the 
Caesar only. The Glacier went into port and anchored and 
the Caesar brought the dock in an hour later and anchored it 
about 300 yards off our port beam. Signalling the dock to let 
gO' the tow line, the Caesar went ahead with starboard helm to 
turn out of the narrow space between the dock and the Glacier. 
A considerable tide was running, which swept her down toward 
our bow and we veered chain to 120 fathoms to make more 
room for her. When she was nearly pointed to pass clear of 
us it suddenly developed that her tow line had not been let 
go from the dock, and this coming taut over her port quarter 
neutralized the helm effect, and she just missed ramming us 
on our port side forward. As it was, she fell across our 
bow, carrying away our bowsprit, which fell overboard, and 
damaging her bridge and awning stanchions and boat davits 
considerably. The actual injury to the ships was so small 
that we could have gone to sea and resumed towing the dock 
within two hours, but it was a narrow escape from a bad 
accident, as the Caesar had way enough on to have cut the 
Glacier down had she struck her in the hull. 


9 


130 


FLOATING DRYDOCKS. 


A week was spent at Singapore to give liberty to our crews 
while coolies coaled the ships. The men had earned a rest and 
extended shore leave, which they got, without regard to con¬ 
duct class, and for which many of them showed appreciation 
in the characteristic manner so well known to commanding 
and executive officers. The Chinese crews of the colliers did 
not abuse their privileges and did not make any extra work 
for the police force on shore. We left Singapore the after¬ 
noon of Tune 28 and entered the China sea for the last leg of 
our long voyage. The southwest monsoon was now well 
established and for several days we had favorable winds vary¬ 
ing in force from light breezes to moderate gales, with much 
rain, thunder and lightning, through which we made good 
progress as the prevailing direction of the wind was nearly 
astern. Then followed lighter and more variable winds with 
smooth seas and considerable blue sky, which period was taken 
advantage of to clean and paint our upper works and get the 
ships into presentable condition for entering port. 

It was the typhoon season, and as we had acquired the 
habit of looking for trouble I think that some of us saw 
unusual colors at sunset and long plumes of cirrus clouds ra¬ 
diating from a point in the horizon almost any time we looked 
for such things. But if we thought we saw them, no harmful 
results followed, and at daylight July 10 we saw what we 
wished to see, the entrance to Subig Bay close ahead and a 
correspondingly satisfactory distance from the Patuxent river. 
At noon the day before, which ended the last whole day’s 
run we were to make, the observed position gave 111 miles 
made good, which is mentioned because of its coincidence with 
the day’s run our first whole day out from Chesapeake Bay. 
Entering Subig Bay, we received a noisy welcome of steam 
whistles and sirens from the Ohio , Rainbozv and some smaller 
naval vessels. Then we “shelled off” from the end of the tow 
and hauled in the heavy water-logged lines for the last time, 
the Glacier first and then the Caesar, leaving the Brutus to 
take the dock to the designated anchorage off Olongapo, which 
was reached and the dock’s anchor let go at 8.55 A. M. We 


FLOATING DRYDOCKS. 


131 

fully expected to moor the dock and strip it of the temporary 
towing appliances before being done with it, but an order had 
been received from the Navy Department that we were excused 
from any more drydock duty as soon as the dock was anchored, 
for which we were thankful, as we had had enough to satisfy 
us. After being only about four hours in that port we got 
underway and left for Cavite, leaving the dock behind with 
no great regret at thus suddenly terminating a long fellowship, 
and with full confidence that we shall recognize it if we ever 
see it again. 



Miles made 

Time. 

Daily 

Passages. 

good. 

averages. 

d. h. 

miles. 

Patuxent River to Las Palmas . 

. 3,844 

56 23 

67.56 

Las Palmas to Port Said. 

. 2,849 

32 OO 

89.05 

Port Said to Suez. 

. 87 

I II 

58.78 

Suez to Singapore. . 

. 4,992 

00 

I 03-38 

Singapore to Olongapo. 

. i,3*7 

II 17 

II2.47 

Totals. 


150 9 

87 -OS 

Ship. 


Coal con- 

Cost 


sumed, tons. 

of coaL 

Glacier . 



$27,224 

Brutus . 



12,594 

Cczsar . 



14,164 

D/>7t)*V . 


923 

4,088 

Totals . 


.. 12,961 

$58,070 


















i3 2 


FLOATING DRYDOCKS. 


THE CAVITE DRYDOCK AT SEA.* 

« 

By Commander F. M. Bennett, U. S. N., Member. 


. The steel floating* drydock built at Baltimore for use in the 
Philippine Islands has been fully described by articles in 
previous issues of this Journal, from which articles I borrow 
the name, though I think it a misfit, because the water is so 
shoal in Manila Bay that this dock could not be used anywhere 
in the immediate vicinity of the U. S. Naval Station at Cavite. 
The act of Congress authorizing its construction is, I believe, 
the authority for fixing the name Cavite upon it. When 
launched, the dock was christened Dewey , in honor of the 
Admiral of the Navy, but in long association with it we of the 
towing squadron always found it awkward to apply that dis¬ 
tinguished name to it, or, indeed, to use any name for such a 
remarkable object, and in daily conversation “it” and “the 
dock” were the more usual and milder terms by which it was 
designated. 

The last chapter in the history of this dock that has ap¬ 
peared in the pages of the Journal was, I think, the article 
by a member describing the self-docking tests that were suc¬ 
cessfully carried out during the month of July, 1905, in the 
Patuxent river. Beginning from that point, I shall endeavor 
to describe briefly some of the engineering problems that arose 
while the dock was in transit from the United States to the 
Far East. Preliminary to such description, however, it is 
necessary to give some account of the special equipment of 
the dock and the towing ships to fit them for the work they 
had before them. At the conclusion of the self-docking tests 
the dock was pronounced a complete success, and so it prob- 

* Reprinted by permission from Journal of thk Amkrican .Society of Naval 
Engineers, Volume XIX, No. 1. 






Cavite Drydock. 


Face 


p. 132 








































FLOATING DRYDOCKS. 


133 


ably was if it could have remained at its moorings in the 
Patuxent river and been used there for docking ships. As a 
sea-going structure it was at that time far from complete, and 
as the long sea voyage was a compulsory service at the begin¬ 
ning of its career, its success at the time referred to cannot be 
regarded as complete when provision for that first service had 
been overlooked. Such important essentials as anchors and 
chains and a capstan for handling them, life boats, and run¬ 
ning lights for a vessel underway, had to be provided, besides 
many minor but necessary articles and fittings before the dock 
could be safely moved. When the builders’ men left the dock, 
only a few days before we intended taking it to sea, it was 
discovered that the shovels in use in the fireroom actually 
belonged to them, and that none had been provided for the 
dock, which incident may give an idea of the many little 
omissions that came to light to distract us during the hurried 
work of preparation for the long sea voyage. 

The shape of the dock was very unfavorable for towing, 
the submerged section being rectangular and presenting a 
square, wall-like surface from seven to ten feet in depth and 
135 feet wide to be dragged bodily through the water. In 
gfood, smooth weather and without aid from wind or currents 
we found four and one-half knots to be about the maximum 
speed we could make with the combined power of the towing 
ships, which speed also was about the limit that the towing 
gear could stand. More powerful ships could have pulled 
more, of course, but any rise in speed would have been met 
by such increased resistance from the dock that very much 
stronger towing lines than any we had would have been 
necessary. In one of the articles published in the Journal 
there were drawings showing several designs of floating docks 
that had been submitted in competition when proposals for 
building this one were invited. At least one of these, if I 
remember correctly, showed a dock with the ends pointed, to 
facilitate its being towed at sea, and it seems, in view of the 
long journey ahead of the Cavite dock, that some such featuie 
should have been included in its design. The large Havana 


134 


FLOATING DRYDOCKS. 


dock, I have been told, was provided with a false, pointed 
bow when it was towed out, and also with an enormous rud¬ 
der, both of much value in keeping it manageable. 

Our greatest troubles in the towing expedition may be di¬ 
rectly charged against the unyielding opposition to progress of 
the square-fronted dock; it was a sufficiently ugly thing to tow 
in good weather, but in high head winds and seas, of which 
we encountered more than our share, it frequently took charge 
beyond any power to control. On such occasions the seas 
and the dock gave a very good presentation of that cataclysm 
upon which young engineers frequently speculate, which is 
supposed to result from the collision of an irresistible force 
with an immovable object, the dock playing the part of the 
immovable object, with temporary success but with ultimate 
failure in all cases. Broken tow lines, the dock adrift, and a 
great amount of time and labor demanded to get hold of it 
again were the results. On some, if not all, of these occasions 
of disaster I am sure we could have retained hold of the dock 
had it been provided with a sea-going bow, but as it was, the 
great seas beating upon the square front of the dock drove it 
backward and put a strain upon our towing gear that could 
not be withstood. A pointed bow, also, would have enabled 
us to make the voyage to the Philippines at considerably 
greater speed, with corresponding reductions in time, and in 
cost of coal and towing gear consumed. 

The vessel selected for the expedition were the supply ship 
Glacier, the naval colliers Brutus and Caesar and the tug 
Potomac. The Glacier and Potomac were manned by naval 
officers and crews and the colliers by merchant officers and 
crews. The principal dimensions of these vessels are: Gla¬ 
cier, 7,000 tons displacement, 353 feet length, 46 feet beam, 
25 feet draught, 4,000 horsepower, 12.5 knots speed; Brutus, 
6,600 tons displacement, 329 feet length, 41 feet beam, 23 
feet draught, 1,200 horsepower, 10 knots speed; Caesar, 
5.000 tons displacement, 322 feet long, 44 feet beam, 21 feet 
draught, 1,500 horsepower, 10 knots speed; Potomac, 785 
tons displacement, 139 feet long, 28 feet beam, 12 feet draught, 


FLOATING DRYDOCKS. 


135 


2,000 horsepower, 16 knots speed. In actual towing in aver¬ 
age weather the Glacier developed (by indicator) about 1,700 
horsepower, the Brutus 1,100 and the Caesar 1,200, or 4,000 
in the aggregate for the three ships, the combined displace¬ 
ments of which were more than 18,000 tons. This seems 
small power to move so much weight and have anything left 
to apply to towing a 12,000-ton drydock, and so it was; but, 
all things considered, the vessels were better suited for the 
work than higher-powered cruisers or battleships would have 
been. Capacity for carrying coal for long periods at sea was 
a consideration that led to the selection of the colliers, and 
the demand for provisions for the expedition for a long period 
selected the Glacier, which ship has cold-storage space for 
1,000 tons of frozen meats. The fuel question was met in her 
case by filling her cargo holds and part of the cold-storage 
space with 2,000 tons of coal. Besides providing cargo coal 
to burn when the bunker supply ran low, these cargoes were 
necessary with all the ships to keep them deep in the water 
and their screws submerged for effective operation. The tow¬ 
ing ships were all single-screw vessels, which was their weakest 
point, as they were clumsy and hard to manage at times 
when handiness would have been a great comfort. 

Except the Potomac, none of these ships had any special 
appliances for towing, and all had therefore to be prepared 
after their selection for the expedition. The chief item in 
this preparation was the installation of a towing machine on 
each vessel. The machines obtained were those made by the 
American Ship Windlass Company of Providence, R. I., and 
were the size designated as No. 5, the largest that is made ex¬ 
cept on special orders. This machine is a two-cylinder steam 
engine, the crank shaft of which, through a pinion and drum 
gear, drives a large drum upon which the wire tow line, two 
inches in diameter and 1,200 feet long, is reeled. The latio of 
the gearing is 5 to 1 ; the steam cylinders are 16 inches in 
diameter and 16 inches stroke of piston. Steani is always on 
this engine when towing, being admitted thiough a partly- 
open regulating valve, and its distinctive feature is in provid- 


FLOATING DRYDOCKS. 


I 36 

mg this steam cushion to take up any sudden jerks on the 
tow line. When any increased strain comes on the line, it is 
drawn out against the pressure of the steam in the cylinders, 
an automatic attachment at the same time screwing open the 
regulating valve until a sufficient increased pressure is admit¬ 
ted to the cylinders to balance the strain on the line. Then, 
when the strain becomes normal again, the machine slowly 
winds in the few fathoms of wire that ran out, the automatic 
gear closing the regulating valve at the same time until equi¬ 
librium between steam pressure and strain on the line is re¬ 
established. So well did the machine work that a mark on 
the line always came back to within a few inches of its origi¬ 
nal place. In rough weather, with the ships pitching and 
wallowing deeply and the strain on the tow line consequently 
very variable, the machine would be working constantly, pay¬ 
ing out wire violently and reeling it back gently, but in fairly 
smooth weather it would sometimes stand for hours at a time 
without a movement. A by-pass valve and operating lever 
are provided for working the machine independently of the 
automatic gear. 

Like most vessels built for commercial purposes, the towing 
ships all had the hand wheel and hand-steering gear on the 
upper deck as far aft as the taffrail, and these were directly in 
the way of the tow lines. On board the colliers the difficulty 
was met by shifting the wheel to the deck below, connecting 
it to its former spindle by sprocket wheels and chain, and by 
building heavy timber casemates over the gear remaining on 
the upper deck. On board the Glacier two deck houses far 
aft made the problem more difficult, and it was solved event¬ 
ually by erecting across the after deck three heavy steel-and- 
oak arches over which the tow line was led clear of the houses 
and the hand wheel. This was not a good arrangement, as 
the wire hawser had to lead up from the towing drum to pass 
over the arches, and, of course, down again toward the water 
when it left the aftermost arch. With the great strain upon 
it, the wire would cut into the hard oak tops of the arches as 
it worked back and forth, and kept us busy patching and 


FLOATING DRYDOCKS. 


C37 


repairing them. 1 here was, fortunately, a quantity pf quar¬ 
ter-inch sheet copper on board, and we discovered that that 
made an excellent covering* for the arches in the wake of the 
tow line; it would get cut through in the course of a week or 
so, but that was a great improvement over having to piece 
and patch on the frames every day. I never knew before 
how tough so soft an appearing metal as copper is, as it cer¬ 
tainly stood more punishment from the tow line than could 
iron or steel plates of the same thickness. If any scientific 
member of this Society doubts this statement I invite him to 
attack a soft piece of copper with a file or with hammer and 
chisel and he will learn something new. 

Twelve steel hawsers, of the size denominated six-inch, but 
rather more than two inches in diameter, were provided for 
use with these machines. They were each 200 fathoms 
(1,200 feet) long, weighed about 7,000 pounds each, and were 
fitted with a thimble and shackle in one end, the other end 
being pointed to pass through a 2-inch hole in the flange of 
the towing drum, where it was secured by clamps. Four of 
these were given to each of the three towing ships. Big as 
they were, they were found insufficient for the heavy strains 
that mid-winter Atlantic weather put upon them, and at the 
first opportunity 8-inch Bullivant steel hawsers, obtained from 
England, were substituted for them. Four of the 6-inch 
wires were made by the Roebling Company in the United 
States; the other eight came from England. 

Twelve 15-inch manila hawsers were also provided. These 
were 200 fathoms long and were very big, handsome lines 
when new, weighing five tons each. Five of them were 
doubled by joining the ends and fitting thimbles in the bights 
thus formed, the two parts of the line being stopped together 
every two fathoms the whole length by stout seizings of rat¬ 
line stuff. As thus made up, each of these spans with its 
thimbles, shackles and seizings weighed over six tons, and 
was, as may be readily understood, an awkward thing to han¬ 
dle, particularly after it had been in use for towing and had 
become thoroughly waterlogged. The other seven 15-inch 


FLOATING DRYDOCKS. 


138 

lines were left single, with an eye for a towing thimble in one 
end only. The shackles, thimbles and other fittings for all 
these lines were made in the equipment shops at the Boston 
Navy Yard, and were enormous for such things, as may be 
realized by looking at Plates 1 and 2 accompanying this 
article. In distributing these manila towing spans for use, 
two of the double and one of the single ones were put on the 
dock, and one double and two single spans on each of the 
three ships. The dock was provided with four bridles, each 
90 fathoms long, made of 2^-inch chain cable, the legs se¬ 
curely bitted at opposite corners of the dock, and a towing 
span shackled in the middle where the legs joined. Two 
bridles were kept in place at each end of the dock, and at the 
end not in use (the stern for the time being) a towing span 
was kept shackled to the bridle and ranged ready for running 
at any time; this to save time in taking the dock in tow after 
a breakdown. We towed the dock from either end indis¬ 
criminately, whichever one was the easiest to get hold of under 
the existing circumstances. To make this possible, a wooden 
trestlework-bridge and derrick for handling the heavy bridles 
and towing spans had been built at the stern end of the dock 
as an afterthought while we were preparing to take it to sea. 

The expedition started from the Patuxent River December 
28, 1905, and passed out at the Capes of the Chesapeake about 
10.30 P. M. the 29th. The Brutus was next the dock and 
had two of the double manila spans, shackled end to end, 
between the 6-inch wire on her towing drum and the bridle 
on the dock. The Caesar was next ahead of the Brutus, 
with one double 15-inch span shackled into the end of the 
wire on her drum, the other end being fast on the bow of the 
Brutus by a chain bridle dipped through its shackle. In get¬ 
ting underway, and for several days thereafter, the Potomac 
towed ahead of the Caesar , but her coal capacity did not per¬ 
mit of continuous work of this kind, and the permanent ar¬ 
rangement was with the Glacier ahead of the Caesaf, the Poto¬ 
mac being in tow herself astern of the dock. For several thou¬ 
sand miles at first the Glacier towed with one of the long 15- 


FLOATING DRYDOCKS. 


139 


inch single manila spans between her 6-inch wire and the bow 
of the C acsar, but after that had been carried away twice and 
cut several times in emergencies she used a double span, the 
same as the other ships. In open water all the ships kept 
nearly all of their 6-inch wire hawsers unreeled from the tow¬ 
ing engine, which made the tow considerably more than a mile 
long from the bow of the Glacier to the stern of the Potomac. 

The first check from bad weather occurred January 4, when 
we were only about 500 miles along on our journey. A moder¬ 
ate gale from S.S.W. and heavy sea prevailed at the time. 
The two colliers were fast to the dock and were facing the 
weather, steaming ahead only enough to keep steerage way, 
but their violent plunging combined with the beating of the 
heavy seas against the dock distressed the towing engines 
greatly, notwithstanding the long tow lines in use. About 
the middle of the afternoon the Caesar’s machine was disabled, 
several teeth breaking out of the drum gear and catching 
between the gear and the pinion on the crank shaft where they 
caused the crank shaft to be lifted out of its bearings, break¬ 
ing the caps, and, of course, putting the machine out of action. 
They managed to bitt the line, and thus held on without losing 
it, and always thereafter the Caesar towed with her line bitted, 
being convinced that the towing machine was inadequate to 
the work of our expedition. The drum gear was temporarily 
repaired by putting in studs in place of the broken teeth and 
thus made serviceable for paying out or reeling in slack wire. 
The teeth of the drum gear were not machined parallel, but 
were slightly tapered lengthwise, just as the pattern had been 
made, to permit of its being drawn out of the sand in molding. 
This was their source of weakness, as they engaged chiefly 
at the thicker ends, and therefore brought on an unequal strain 
that caused those ends to chip and break; this happened to. 
the towing machines on all three ships to a greater or less 
extent and led to the complete disablement of the machines 
of the Brutus and Caesar. 

About a week later, January 12, the dock broke adrift from 
ns for the first time. The wind was only moderate, but a 


140 


FLOATING DRYDOCKS. 


very heavy sea had been running all day, causing the ships 
to roll abominably, and no good cause for the towing gear to 
fail existed; but late that night the 6-inch wire line in the 
train between the Brutus and the dock parted and let the 
dock go adrift. I shall not in this paper attempt to describe 
the toil and anxiety that such an accident brought with it, 
but they may be readily imagined by any one reflecting upon 
the mass and weight of wet lines to be hauled on board, the 
clearing and preparation of them for use again, the handling 
of heavy shackles in the dark, and then the task, sometimes 
really dangerous, of getting hold of the drifting and unman¬ 
ageable dock. In the whole history of the expedition the 
dock was adrift six times—four times in rough seas, once in 
a calm when there was absolutely no- provocation for it, and 
once as an incident of shortening the tow lines preparatory to 
entering port. The parts of the towing gear that failed and 
thus permitted these accidents were the 6-inch steel hawsers, 
twice; a double 15-inch manila span, once; and once each 
for a 2-inch chain bridle, a double shackle and a triangular 
shackle. Only a few days after we had resumed towing after 
the breakdown above mentioned, the single 15-inch manila 
line between the Glacier and Caesar parted, but we did not 
reckon that a calamity, because two ships remained towing 
the dock and the general progress was not stopped while the 
Glacier repaired damages. The same thing happened again 
at a later period in the voyage, after which the use of the 
single 15-inch lines was discontinued. 

Beginning January 24 we had a period of almost a month 
of head winds and discouraging conditions generally. We 
were about the middle of the Atlantic Ocean trying to make 
a course east (true) along the 28th parallel of latitude, and 
met the wind from N.E., east, and S.E., almost without 
change and of such force as to impede us greatly, while fre¬ 
quent gales gave us a vast amount of hard labor and trouble. 
Daily “runs” of less than forty miles became common, and 
one day the noon position by observation put us twenty-four 
miles west, or astern, of the place we had been in the previous 


FLOATING DRYDOCKS. 


HI 


noon. January 25, while facing a moderate to fresh gale 
from S.E., the Glacier had to cut off from the tow to reduce 
the strain on the lines of the other ships, but that night the 
great strain and heavy sea overcame the towing machine on 
the Brutus , which was totally disabled. Teeth were stripped 
off the drum gear around almost half its circumference, the 
crank shaft was thrown out of its bearings and bent, both 
connecting rods badly bent, and other parts either broken or 
bent beyond repair; the 6-inch wire line parted near the tow¬ 
ing drum at the same time, and of course the dock was adrift. 
The weather continued so bad that it was forty-nine hours 
before we got the dock in tow again, during which time it 
had drifted about 100 miles back towards the United States. 
Only twenty-nine hours later it broke adrift again by the 
parting of a 2-inch chain bridle over the stern of the Brutus, 
and was at large a day and a half before lines were gotten to 
it and the towing hawsers hauled over ready to use. 

In the accidents that had happened thus far the longest 
pieces of the broken 6-inch wire lines had been hauled on 
board the dock, and these were spliced together, making one 
span about 250 fathoms long, which was put into the place of 
a damaged ioo-fathom 15-inch manila span between the Brutus 
and the dock, the forward end of it being shackled into a new 
6-inch wire line on the Brutus. This line, owing to the Brutus 
towing machine being disabled, was nearly all paid out, the 
inboard end being bitted and the bitts backed to the mainmast 
by chain cables taken from the anchors. There was thus a 
clear run of tow lines of over 3,200 feet, or more than half a 
mile, from the Brutus to the dock, the great length and weight 
of which was its own protection, and there were no more 
breakdowns as long as it was in use. As made up this time, 
the whole length of the tow from the Glacier to the Potomac 

was more than a mile and a half. 

While toiling forward against head wind and seas with 
enough troubles of her own, the exigency of the Potomac in 
regard to coal began to force uncomfortable attention. As 
before stated, that vessel was usually towed, but in very rough 


T 4 2 


FLOATING DRYDOCKS. 


weather she had to cast off and take care of herself, and con¬ 
sequently had to keep enough coal on hand to enable her to 
weather a gale, besides sufficing for her daily needs. We 
watched her noon reports showing the steady diminution of 
her supply from day to day and hoped fervently for a let-up 
in the merciless wind that would make it possible for her to 
come alongside the Glacier; but no such abatement came nor 
seemed probable, until finally, when the situation forbade any 
more waiting, the Glacier cast off from the head of the line 
and devoted herself to the Potomac for the next six days. 
At first we took her alongside and gave her fifteen tons of coal 
in about half an hour, but then had to desist, as the sea was 
so heavy that both vessels were sustaining serious damages. 
Nearly a day was spent in trying to put into operation an over¬ 
head wire transporter, but the violent motion of the ships, the 
pitching of the Potomac especially, rendered this scheme en¬ 
tirely impracticable. Then, with the Potomac in tow, we got 
an under-water line in operation and began sending her coal 
in bags, hauled through the water. That was slow at first, 
and during two days we gave her only about as much as she 
burned, but the next day, with experience and with much 
heavier gear to work with, we gave her four days’ supply. The 
next morning the weather was moderate for a few hours, which 
we took advantage of to get her alongside, and gave her 
enough to make her safe for two weeks longer. It was a hard 
and trying week, but valuable in showing that men can do 
almost anything when they have to. 

The dock had now become a source of anxiety because the 
people on board it thought it threatened to fall apart. The 
end pontoons were secured to the overhanging side walls of 
the central pontoon by a system of plates, angle irons and bolts, 
and weakness had developed in the riveted angle irons that 
secured the vertical fastening plates to the deck of the end 
pontoons. The dock was very buoyant and always had con¬ 
siderable motion, both rolling and pitching, in a seaway. This 
brought a constantly varying series of stresses and strains 
upon the riveted joints spoken of, which being continued for 


FLOATING DRYDOCKS. 


143 

\\ eelcs w ithout 1 cst as the dock pitched about in the rough sea 
began to show disastrous results. Many of the rivets were 
worked loose (6,000 out of 7,000 had to be renewed), and this 
loosened the angle irons so that they had considerable play as 
the ends of the dock rose and fell, the mischief, of course, 
multiplying as the amount of loose motion increased. There 
was yet strength enough in the joints to resist considerable bad 
weather, but it was not prudent to let the injuries go on in¬ 
creasing, and the commander of the expedition decided to 
seek the nearest port where repairs could be made. Accord- 
ingly we went to Las Palmas, in the Canary Islands, and there 
had the dock strengthened so that it was more seaworthy than 
when we left home with it. But for this work I fear we would 
have lost the dock, as soon afterward we had a gale in the 
Mediterranean Sea worse than any we saw in the Atlantic, and 
which, I believe, would have taken the end pontoons off the 
dock had they been allowed to remain in their crippled con¬ 
dition. 

When we arrived at Last Palmas we were just fifty-seven 
days from the Patuxent river, and had dragged the dock in 
that time 3,844 miles, or considerably more than the distance 
across the Atlantic could we have applied it to a direct course. 
Had it not been necessary to repair the dock we should have 
been obliged to stop at the Canaries anyhow, because our 
long period at sea had almost exhausted the supply of coal 
and water on the dock. We started with what was considered 
ample to reach Port Said, but the many breakdowns had 
caused the use of the capstans and other steam machinery on 
the dock much more than had been expected, and, as no con¬ 
denser had been provided, a great amount of fresh water had 
been lost in the form of exhaust steam. There was an evap¬ 
orator on the dock, but without a condenser for the steam 
that passed through it it is doubtful if it produced as much 
water as was required in the form of steam to evaporate the 
sea water in the first place. Some scholarly member of this 
Society familiar with thermal units and their habits may be 
able to cipher this out otherwise, but to an ordinary mind 


144 


FLOATING DRYDOCKS. 


this peculiar form of an evaporator looks remarkably like a 
device for making something out of nothing. At any rate, 
its use was discontinued when it became evident that it caused 
a loss and not a gain in the fresh-water tanks. 

Having referred to people on board the dock, I will answer 
a question that has been asked me a number of times already, 
and say that there always were men on the dock when i‘t was 
being towed at sea—more than thirty of them, in fact. There 
were nine men, employees of the Bureau of Construction and 
Repair, who constituted a permanent crew for the dock to 
attend to its care and operation when it reached its destina¬ 
tion. Then there was a regular crew shipped for the voyage 
the same as the crew of any merchant ship, composed of sail¬ 
ing master, two mates, cook, steward, twelve seamen (after¬ 
ward increased to eighteen), a rigger and a few others, such 
as messmen and telegraph operator. There was nothing 
perilous in their position; on the contrary, they were un¬ 
doubtedly safer than they would have been on a real ship, and 
they were certainly more comfortable in rough weather than 
any of us were on the towing ships. 

April 7 to 9, when in the eastern basin of the Mediterranean 
Sea about 200 miles east of Malta, we encountered a gale from 
eastward and southward that at one time reached the force of 
a whole gale (10 by the Beaufort scale) and raised a heavier 
sea than any that we had experienced in the Atlantic Ocean. 
The Glacier , as she had done on several previous occasions, 
cast off to reduce the strain on the tow lines, but the gale 
steadily grew in force, and the second day, April 8, the dock 
broke adrift by the parting of a large shackle that joined the 
legs of the towing bridle to the first span. The dock drifted 
rapidly to leeward broadside to in the trough of the sea and 
achieved her maximum roll on this occasion, only eight de¬ 
grees, but owing to the great height of the side walls above 
the water this looked very much more to an external observer. 
As a lee shore was only 200 miles away the situation was 
more critical than when the dock was adrift in mid ocean, 
but after it had been loose twenty-three hours and while the 


floating drydocks. 


H5 


sea was yet heavy the Brutus, aided by the Potomac, got a 
me to it and was able to check drifting to leeward though 
unable to tow it against the weather. By the ioth the storm 
had blown itself out and we all resumed towing* to the east- 
ward. The evening of the nth, when towing in a smooth 
sea with no wind, a double i S -inch manila span between the 
Bratus and the dock suddenly parted, from no cause whatever 
except what is popularly known as “pure cussedness,” and 
set the dock adrift again. The situation offered no difficulties 
in picking up the dock, but the work of hauling in the heavy 
lines, ranging them clear for running, and running them again 
in making up the tow, kept us busy nearly all night, and 
it was after two o’clock in the morning before we were steam- 
ing ahead on the course again. 

The passage of the dock through the Suez Canal was effected 
with less trouble than anticipated, and there would have been 
practically none had not an unusually strong beam wind forced 
it out of one of the sidings where it was moored and against 
the bank on the opposite side, blocking the canal for several 


hours. It was towed through by two powerful tugs of the 
canal company in tandem ahead, with the Potomac astern to 
push and to prevent the rear end from yawing into the banks. 
The dock was in the canal four and one-half days, but was 
actually under way only thirty-five hours, considerable periods 


having been spent at anchor in Lake Timseh at Ismailia and 
in the Great Bitter Lake to allow steamers to pass both ways 
and avoid stopping traffic. The Potomac rendered such ex¬ 
cellent service here that it made up for all the trouble she had 
caused us in the Atlantic. She returned to the United States 
from Suez. 

At Port Said we got the 8-inch steel hawsers that had been 
ordered from England, and the Brutus and Caesar put them 
on their towing drums in place of the 6-inch wires. In mak¬ 
ing up the tow at Suez the manila spans between the Brutus 
and the dock were discarded and their place filled by 105 
fathoms of 2^-inch chain taken from the spare bridles on the 
dock. One end of this chain was shackled to the dock’s 
10 


146 


FLOATING DRYDOCKS. 


bridle and the other into the end of the 8-inch wire from the 
Brutus' towing drum. I neglected to state in the proper 
place that at Las Palmas we received from the United States 
spare drum gears for the towing engines, and those machines 
on the Brutus and Caesar were put in good order again. 
The weight of the chain span just described was fifteen tons 
and of the 8-inch wire joined to it almost five tons, the two 
forming a catenary so deep that there was no danger of any 
power we had ever bringing it up taut. The Caesar had a 
double manila span between her 8-inch wire and the Brutus, 
and the Glacier used another one to the Caesar from a new 
6-inch wire on her towing machine. With the towing train 
thus strengthened we felt free to steam at full power, and did 
so with such excellent results that we towed the dock from 
Suez to Singapore, 5,000 miles, in forty-eight days, without a 
break or accident of any sort to the towing gear, and with 
only one stop, of two hours’ duration, to replace a gasket 
blown out on the Glacier. 

In entering the port at Singapore the combination of a very 
dark night and a swiftly-running spring tide threw the squad¬ 
ron into some confusion while shortening in the lines, and 
when the ships got straightened out clear of danger from each 
other the dock was found to be adrift. Contrary to all the 
rule of dynamics, the big double shackle joining the chain 
span to the dock’s towing bridle had parted, but how it hap¬ 
pened was not at all clear. The dock was anchored, and after 
daylight was gotten under way and towed into port with no 
greater loss than a few hours’ time, but as it had taken us six 
months to get that far, time had become a matter of small 
value to us. A stop of a week was made at Singapore to coal 
and water the ships and to give the crews a run ashore. Then 
we resumed our voyage, proceeding northeastward into the 
China Sea, where the best long run of the whole trip was made, 
the distance of over 1,300 miles to Olongapo being made at 
the average rate of H2 l / 2 miles per day. The best day’s run 
of the whole voyage was 152 miles, made June 9th in the Bay 
of Bengal, where a current of at least forty miles per day 





CQoijxwt omccn. 


Plate I 


MAWI "• "• 3971 - 36 . 





























































































































































































































































. 





















floating drydocks. 


H7 



Plate II.—Details. 






























































































































































































































I 


148 


FLOATING DRYDOCKS. 


favored us; the worst day’s run was, as before mentioned, in 
the Atlantic where we achieved minus 24 miles one day steam¬ 
ing against a head wind and sea. We arrived at Olongapo in 
Subig Bay early in the morning of July 10, 1906; the towing 
ships let go one after the other, the dock was anchored, and a 
few hours later we left it there without regret and returned 
to the world that we had been out of for more than half a 


y ccti. 

Passages. 

Miles 

made good. 

Time. 

Daily 

averages. 



Days. 

Hours. 


Patuxent river to Las Palmas. 

• • 3-844 

56 

23 

67.56 

Las Palmas to Port Said. 

.. 2,849 

32 

00 

89.03 

Port Said to Suez. 

.. 87 

I 

11 

58.78 

Suez to Singapore. 

.. 4,992 

48 

7 

103.38 

Singapore to Olongapo. 

•• L 3 I 7 

11 

17 

112.47 

Totals. 

. -13.089 

150 

9 

87.03 


Ship. Coal consumed. Cost of coal. 

Tons. 

Glacier . 5,136 $27,224 

Brutus . 3,664 12,594 

Caesar . 3 >238 14,164 

Dewey . 923 4,088 


Totals. 12,961 $58,070 


Editor’s Note. —Lieutenant Commander Bennett’s accounts 
of the towing of the floating drydock Dezvey to its destination 
are most interesting and instructive. The hardships and trials 
of the trip are most vividly pictured, and the things which 
should be avoided are strongly and clearly pointed out. From 
the clear and full description of the whole matter it is probable 
that the trip could be repeated with only a fraction of the 
trouble experienced and at an appreciably reduced cost. 

One thing has been fully demonstrated beyond further ques¬ 
tion, and that is that a floating drydock can be towed anywhere 
and under any circumstances. 



















FLOATING DRYDOCKS. 


149 


It also appears that the fewer the towing vessels the power 
is concentrated in the better the control of the tow will be. 
The longer the tow line the less the danger of parting the 
same. That in bad weather there is liable to be more lost 
than made by attempting too much speed. 

This trip was a history-making affair which was watched 
with the greatest interest by all nations. It marks a long ad¬ 
vance in both maritime and military possibilities, and as time 
dims the hardships of those who accomplished it let us hope 
that they will be more than recompensed by the recollection 
of their remarkable feat. 


FLOATING DRYDOCKS. 



150 


THE NAVAL FLOATING DOCK—ITS 
ADVANTAGES, DESIGN AND CONSTRUCTION * 
By Leonard M. Cox, M. Am. Soc. C. E. 


With Discussion by Messrs. George B. Rennie, J. R. 
Baterden, Cecil H. Peabody, C. Colson, A. C. Cun¬ 
ningham, Lyonel Clark, Edward Box, B. C. 
Laws, L. J. Le Conte, W. H. Pretty 
and Leonard M. Cox. 


A nation’s foreign commerce is a measure of its wealth. 
Foreign commerce is carried on by means of ships; and ships 
require harbor and docking facilities. Other conditions being 
equal, that port offering the best facilities for cleaning and 
repair work, in addition to deep water and protected berthing, 
will reap the largest measure of prosperity. The speed of a 
ship, for a given coal consumption, is a factor of its earning 
capacity, and marine growths foul a ship’s bottom, affecting 
thereby its speed. Iron and steel corrode in salt water, and 
must be given protective coverings; these coverings last but a 
short time in active service, and require periodical renewals. 
Ships are likely to be damaged by grounding or by collisions, 
and access to their bottoms must be provided in order to make 
the necessary repairs. In fact, from the very beginning of sea 
commerce the question of repair docks has been of vital interest 
to merchants and ship owners as well as to governments, and, 
in view of the great movement toward commercial expansion 
which has marked the last decade, it is safe to assume that this 
interest will at least continue, and that a discussion of the 
subject will not fail to be of interest to an engineering society. 






* Presented at the meeting of December 5, 1906, and reprinted by permission from 
Transactions American Society of Civil Engineers, Vol. LVIII, p. 79 (1907). 












FLOATING DRYDOCKS. 


151 

Historically, three epochs in ship-repairing appliances are 
marked: By the use of tide flats, when the Phoenicians 
careened their vessels on the shores of the Mediterranean; by 
the citide mud docks of the Greeks; and, by the (legendary) 
use by the North Country captain, of the hulk Camel as the 
forei unner of the floating dock. From these crude prototypes, 
the evolution of our modern structures followed. Increased 
demand and more exacting -requirements have brought about 
improvements of design and of methods of operating; but, as 
regards general type and working principles, very little that 
is really new can be claimed. 

Repair docks may be considered under four heads: The 
Graving Dock; the Floating Dock; the Marine Railway; and 
the Lift Dock. 

The Graving Dock or Drydock .—The graving dock is an 
excavation in the foreshore of a harbor, cut off from the basin 
by portable gates or caissons. It may be lined with timber, 
stone, concrete or combinations of these materials. After the 
ship is floated into the dock and centered over the blocking, 
the gates are closed, and the water is removed by pumps. 

The Floating Dock .—The floating dock is a hollow struc¬ 
ture, of wood, iron or steel, capable of being submerged by the 
simple admission of water to its interior and of being raised 
to its lightest flotation again by means of pumps. When the 
dock is submerged the ship is floated into position, the pumps 
are started, and the dock, with the ship on its deck, is raised 
until the ship’s bottom is out of the water. 

The Marine Railway .—The marine railway consists of in¬ 
clined ways extending for some distance under the water. 
The ship is received on a cradle and hauled up on the shore. 

Lift Docks .—Lift docks include those devices which consist 
essentially of a platform capable of being raised and lowered 
by hydraulic or other power. 

The limits of this paper confine consideration to the floating 
dock proper, but no discussion of one particular type of dock 
would be complete without some attempt to set forth the con¬ 
siderations governing the choice of types. 



152 


FLOATING DRYDOCKS. 


\ 


One of the results of many investigations prosecuted by 
intending builders is the apparent division of engineers and 
naval architects into drydock and floating dock adherents. It 
is evident, however, that each type has its own particular field 
of usefulness which the other cannot with advantage fill, and 
that, for a given set of conditions, a careful study of both 
types, as applied to the special requirements of the case, must 
govern the choice. ^ 

For commercial purposes, the advantages of the stationary 
or basin drydock consist in the fact that it can be used in 
shallow harbors, and that the ship, when seated, is safe. Its 
disadvantages lie in its greater first cost (except in the case of 
timber docks in favorable foundations) ; the greater quantity 
of water to be pumped; the lack of good ventilation and proper 
light under the ship’s bottom; and the area of land required. 
The floating dock has the advantage of smaller first cost; no 
land space required; the ability to maintain the ship in virtually 
the same shape as when waterborne; and finally, its mobility. 
Its disadvantages are the possibility of accident (the chances 
of which, however remote, can never be entirely eliminated) ; 
the necessary occupation of useful water front; and the greater 
depth of water required for operation. 

From the standpoint of naval requirements, the case is differ¬ 
ent. Sir William H. White, Hon. M. Am. ‘Soc. C. E., in the 
discussion on drydocks,* at the International Engineering 
Congress, at St. Louis, in 1905, says: 

“A modern ship, especially a modern warship, obviously re¬ 
quires careful handling in docking. An armored ship with 
hundreds of tons of armor on her sides, and of great width, is 
built with a bottom that is comparatively an egg-shell, and, 
unless properly supported, there are enormous risks in docking 
such a structure. It is quite easy to crush up the bottom of 
such a ship unless great care is taken. The case of the U. S. 
Cruiser Columbia, when docked at Southampton, is well 
known. The spacing of the blocks was just such as would 
have been practiced with ordinary merchant ships, but it was 


♦Transactions Am. Soc. C. E., Vol. LIV, Part F. 



FLOATING DRYDOCKS. 


153 


not suitable to the light structure of the warship and the results 
were anything but satisfactory. The speaker has been in the 
double bottom of a large ironclad docked in a Government 
dockyard in England, where, owing to want o;f care, certain 
portions of the structure were pushed up in relation to others, 
and the light framework at the bottom was squeezed in a very 
uncomfortable manner.” 

The modern warship has a delicate framework of small local 
resistance, and, as it represents an outlay of several millions of 
dollars, the question of subjecting it to any sort of risk is one 
which calls for serious consideration. For docking ships of 
this character the consensus of engineering opinion seems to 
favor the basin dock, because of its safety, its rigidity and the 
smaller liability of error from the personal equations of oper¬ 
ators. One of the objects of this paper is to show just how 
far the latest practice in floating-dock construction has gone 
toward minimizing, or even eliminating, these objections while 
developing the peculiar advantages of the type. 

First Cost of Docks .—Ten years ago, or more, the timber 
drydock was much favored in America on account of its small 
first cost and the short time required for construction. As far 
as naval purposes are concerned, however, the question of ma¬ 
terial for docks appears to have been settled in favor of 
masonry, since experience with timber docks established the 
fact that they were temporary structures at best, and that the 
small first cost was more than offset by the large charges 
against maintenance. As compared with the timber drydock, 
the first cost of the floating dock is greater; but, as compared 
with the cost of the modern masonry dock capable of docking 
the same ships—and the policy of the Navy Department for 
the last ten years has been in favor of masonry docks—the 
floating dock costs about the same and in some instances less. 

The first cost of masonry drvdocks depends to a great extent 
upon the nature of the foundation encountered, and the nec¬ 
essary uncertainty of this factor often renders it impossible 
to prepare accurate preliminary estimates. The cost of a dry- 
dock varies according to different localities, labor conditions 


*54 


FLOATING DRYDOCKS. 


and prices of materials; and, in consequence, it is impossible 
to make a general comparison of cost between the floating and 
the stationary structures. Whenever such comparison is at¬ 
tempted, however, docks of essentially the same capacity should 
be selected. To arrive at an equitable comparative rating re¬ 
gard must be had for the lifting capacity, the clear width 
of entrance, the available length and the maximum draught 
of water over the blocks. A drydock will support the heaviest 
ship that can be placed in its basin, while a floating dock will 
lift only the load for which it is designed. A floating dock 
has an available depth of water equal to the height of the side 
walls, less the height of the keel blocks, plus the required free¬ 
board, while the depth of a drydock is fixed by the depth of 
water over the sill. A floating dock can lift a ship whose keel 
length does not exceed the length of the blocking, whereas the 
capacity of a drydock is limited by its own length. As regards 
clear breadth between walls, that dimension is usually the same 
throughout the length of the floating dock, while in dry docks 
the width at entrance must govern. In making comparisons, 
the lifting capacity of the floating dock may be disregarded, 
as its dimensions usually govern a ship’s weight, and a dock 
of a certain lifting capacity would rarely be designed with 
such dimensions as would admit a ship of excessive weight. 

The most important particular, however, is the matter of 
breadth. At present, the largest and heaviest battleships are 
of the new i6,ooo-ton type, 450 feet in length, 76 feet 10 inches 
in breadth, and having a mean draught of 24 feet 6 inches. 
That the limit in size has not yet been reached is evident from 
the fact That even now tentative plans for 18,000-ton ships are 
being proposed, while even 20,000-ton ships have been advo¬ 
cated. It is reasonable, perhaps, to suppose that such increase 
in size will be accompanied by some increase of beam, and it 
is interesting to note that of the American naval drydocks now 
constructed only four could take ships of these dimensions, 
and of these four those at Portsmouth and Boston have only 
recently been completed, while Dock No. 3 at the New York 
Navy Yard and the Puget Sound Navy Yard dock afford such 


FLOATING DRYDOCKS. 


155 


narrow margin between the entrance walls and the ship that it 
is doubtful if constructors would care to undertake the risk in¬ 
volved in docking. When those now being constructed are 
completed, five docks, amply large for such ships and with a 
fair margin for future expansion, will be added to this list. On 
the whole, then, it is here proposed that, in comparisons of the 
cost of the two types, the floating dock be regarded as equiva¬ 
lent to a drydock having a width at entrance the same as the 
•clear width between its side walls, having a length exceeding 
its own by at least 100 feet, and having a maximum depth of 
water over the keel blocks equal to the maximum depth attain¬ 
able in the floating dock. On this basis the dock Dewey, for 
instance, could be compared with Dock No. 3 at the Norfolk 
Yard, Dock No. 1 at Charleston (both under construction), 
and with the new Boston and Portsmouth docks. Table 1 
gives the first cost of the naval docks of the United States. 

Table 1 .— First Cost of United States Naval Drydocks. 

BASIN DOCKS. 


Location. 

Material. 

Date of completion. 

Original 

cost. 

Remarks. 

Boston, No, 1. 

Masonry. 

1833 

$972,717.29 


Boston, No. 2. 

Masonry. 

i9°5 

1.105,665.27 


New York, No 1. 

Masonry. 

1851 

2,003,498.05 

Rebuilt in con 

New York, No. 2. 

Timber. 

1890 

505,019.24 

New York, No. 3. 

Timber. 

1897 

554,707 08 

Crete, 1900. 

New York, No. 4. 

Masonry and 
concrete. 

Under construction. 

757,800.00 

Body only. 

League Island, No. 1. 

Timber. 

1891 

548,700.00 


League Island, No. 2. 

Concrete and 
masonry. 

Under construction. 

1,301,111.76 


Norfolk, No. 1. 

Masonry. 

1834 

943,676.00 


Norfolk, No. 2. 

Timber. 

1889 

504,980.00 

Body only. 

Norfolk, No. 3. 

Concrete and 
masonry. 

Under construction. 

876,776.00 

Port Royal, No. 1. 

Timber. 

1895 

449.437-°9 


Mare Island, No. 1. 

Masonry. 

1891 

2.772,322.08 


Mare Island, No. 2. 

Concrete and 
masonry. 

Under construction. 

1,385,000.00 


Puget Sound, No. 1. 

Timber. 

1896 

632,636.33 

Body only. 

Charleston, No. 1. 

Concrete and 
masonry. 

Under construction. 

906,351.86 


FLOATING DOCKS. 


Algiers. 



Steel. 

1902 

$809,713.52 j 


Dewey . 



Steel. 

i9°5 

i,i43.959- 68 j 

_ 


Noth. —In the case of the Norfolk, No. 3, Charleston, No. 1, and New York, No. 4, docks, the 
bodies were let independently, the caissons, machinery, and pump wells to follow Bids on the 
Charleston caisson were from $105,000 to $85,000 ; it was estimated, however, that the work could 
be done at a lower figure by a Navy Yard department, and therefore no contract was awarded. 

The cost of the Mare Island and League Island new docks will very probably be increased before 
being placed in commission. 


















































FLOATING DRYDOCKS. 


156 

An important matter to be considered in the first cost of a 
floating dock is the preparation of the site to receive it. Ex¬ 
pensive dredging may be required, and more or less permanent 
moorings and expensive shore connections must be provided. 
This work should properly be charged to first cost in any com¬ 
parison with the cost of stationary docks. 

Time Required for Construction .—As regards the time re¬ 
quired to construct, it would seem that the floating dock has 
a decided advantage. The granite dock at Portsmouth, N. H., 
required 6 years to complete; the granite dock at Boston, 6 
years; and the docks at League Island and Mare Island, con¬ 
tracted for in 1899, are yet unfinished. The small granite dock 
at the Boston Navy Yard was commenced in 1827 and finished 
in 1833, and the small dock in the New York Navy Yard was 
under construction from 1841 to 1851. Of the naval timber 
docks, No. 3, at the New York Navy Yard, required 5 years; 
the Port Royal dock, 4 years; and the Puget Sound dock, 4 
years. 

In a most excellent paper, read before the Institution of 
Civil Engineers, in August, 1905, by Mr. L. E. Clark, of the 
firm of Clark and Standfield, the time of construction of a num¬ 
ber of floating docks designed by that firm is given; and this 
information has been used in Table 2 : 


Table 2. —Data Relating to Floating Docks. 


Dock. 

Lifting capacity, 
in tons. 

Weight of hull, 
in tons. 

Date of 
completion. 

Time required 
to build. 

At Havana. 

10,000 

4,260 

1897 

11 months 

Pola. 

15,000 

5,200 

1904 

23 

Stettin.. 

11,000 

4,002 

1897 

7 i “ 

Port Said... 

3,ooo 

L 5 I 4 

1904 

7 ‘ ‘ 

0 

To which may be added : 




Algiers,. 

18,000 

5,850 

1902 

27 months. 

Dewey . 

V- 

20,000 

9,200 

1905 

23 


Of course, the time element, as well as every other factor 
which enters into the question, is largely dependent on local 
conditions; hence no true generalization can be made. 



































FLOATING DRYDOCKS. 


157 


Maintenance Charges .—The granite or concrete dock should 
require virtually no maintenance, except that due to the or¬ 
dinary wear and tear on the machinery, caisson and auxiliary 
appliances. The floating dock, on the other hand, requires con¬ 
stant attention, including frequent self-docking, painting and 
cleaning. To the ordinary repairs must be added those due to 
accidents to the hull—an item which cannot be estimated in 
advance. 

Table 3. —Data Relating to Repairs of Drydocks.* 


Location. 

Period. 

Dock. 

Accessories. 

Total. 

Boston. 

1889-99 

$4,158.25 

$55,050.09 

$59,208.34 

New York, No. 1. 

1889-99 

1,815.80 

11,698.01 

13,513-81 


f 

In progress, 



New York, No. 2. 

1890-99j 

$300,000.00 




expenditure. 

2,233.63 


New York, No. 3. 

1897-99 

171,360.76 

173 , 594-39 

League Island. 

1891-99 

70,721.38 

7 . 874.39 

78 , 595.77 

Norfolk, No. 1. 

1889-99 

260.20 

29,912.73 

30,172.93 

Norfolk, No. 2. 

1889-99 

54,010.77 

39 , 432.79 

93 , 443.56 

Port Royal. 

1895-99 

23,766.72 

1,664.00 

25,430.72 

Mare Island. 

1890-99 

4,363.62 

19,912.63 

24,276.25 

Puget Sound. 

1897-99 

328.12 

11,025.00 

ir , 353 . 12 


* Annual Report of Chief of Bureau of Yards and Docks, 1899 


The expense of self-docking operations varies with the design 
and with the ability of the operator, but experience would indi¬ 
cate that it is not necessary to overhaul the bottom of steel 
docks at smaller intervals than from 5 to 8 years. The old 
idea that steel is more liable to injury by corrosion in sea water 
than iron, seems to be losing ground, and authorities are not 
wanting for the statement that there is little, if any, difference 
in the deterioration of the two metals, if the steel has first been 
thoroughly cleansed of mill-scale. Indeed, no less an authority 
than Sir William H. White has given his experience as follows: 

“If the manufacturer’s scale (black oxide) is entirely re¬ 
moved, and equal care taken in protecting the surfaces with 
paint or composition, iron and steel have about the same rate of 
corrosion, the steel wearing somewhat more uniformly than 
the iron.” 

As a floating dock is not intended to show speed qualities, 
the bottom is ordinarily only cleaned for the purpose of pro- 






























FLOATING DRYDOCKS. 


158 

tecting the plating. A heavy sea-growth, however, seems to 
afford the best protective covering that can be had, and there is 
a question as to the advisability of removing it until the in¬ 
creased weight becomes of appreciable importance. The expe¬ 
rience of Assistant Naval Constructor W. G. DuBose, U. S. N., 
in charge of the self-docking of the Pensacola dock (Havana 
dock), is of great interest. In his official report of the opera¬ 
tion, he says: 

“The under-water plating of these pontoons was found to 
be completely covered to a depth of 8 inches or more with a 
growth of large oysters, barnacles and various shell growths. 
By weighing the foreign matter from various places on known 
areas, it was found that the average weight of shell growth on 
the bottom plating was 9 pounds, and on the side plating 4 
pounds per square foot. The total weight of shell growth re¬ 
moved from these three pontoons was 99 tons. In addition, 
it is estimated that about 30 tons of mud, scale and other dirt 
was removed from the inside of the pontoons. This growth 
formed an almost perfect protection for the plating, which 
was found to be in excellent condition throughout, with prac¬ 
tically no corrosion. It is not believed that self-docking of the 
dock will again be necessary for at least five or six years.” 

Based on the experience of the contractors in the acceptance 
tests, the probable maintenance charges for the Dezvey could 
be estimated as follows, assuming that it is thoroughly over¬ 


hauled every fifth year: 

Expense of self-docking. $10,000 

Three coats of paint complete. 27,000 

Cleaning bottom. 1,000 

Cleaning interior. 2,000 

Maintenance of fixed equipment. 5,000 

Total. $45,000 


For one year, $9,000, or 0.72 per cent, of the first cost. 

The average cost of maintenance of nine docks, cited by Mr 
Clark in the paper previously referred to, is 1.12 per cent, of 
the first cost. As .Mr. Clark has done more to advance float¬ 
ing-dock design than any other one person, and as he has had 
ample opportunity for observing a large number of docks built 









FLOATING DRY DOCKS. 


159 


according to the designs of his firm, his experience must be 
regarded as of great value. 

Operating Expenses. —The attendance required in docking a 
cruiser of the Colorado class in a stationary dock is slightly 
less than that for docking the same ship in a floating dock. 
On a floating dock an engineer and fireman are required for 
each pumping element, besides one or two valve men, whereas 
the pumping plant of a drydock would require only one man— 
with the proper proportion of the expense of the central power 
plant. The quantity of water to be removed from a drydock 
depends upon the size of the ship docked, and is greater for the 
small ship than for the large one; while in the case of the 
floating dock the pumping required is directly proportional to 
the weight lifted. On this account the first cost of a pumping 
plant required to dock a maximum ship and a minimum ship 
in a specified time would be greater for the drydock, and the 
coal consumption should also be greater. As a matter of fact, 
however, the coal consumption depends so much upon the oper¬ 
ator that little benefit can be derived from comparisons. 

As the most economical condition for pumping, in the case 
of a drydock, is when docking the largest ship it is capable of 
holding, the following comparison of the quantity of water to 
be removed in both types is based on the U. S. S. Colorado as 
docked by the Dewey, and the case of the same ship if docked 
in Dry Dock No. 4 (now under construction) at the New York 
Navy Yard. As the Colorado is 504 feet between perpendicu¬ 
lars, and as the drydock in question is only 550 feet on the 
floor, it will be seen that the dock prism is about as nearly filled 
as practicable. 

Dry Dock No. 4, New York Navy Yard: 


Total water contained in prism of dock 58,700 tons - 
Displacement of Colorado ' in docking 

trim. 13,500 tons. 

Water to be removed in docking. 45 > 200 tons * 

Water to be removed to arrange blocks 

after docking. 58,700 tons. 


Total water to be removed. 103,900 tons. 







i6o 


FLOATING DRYDOCKS. 


Floating Dry dock Dewey: 

Total water pumped from floating dock 
Dewey from 30 feet over deck, rais¬ 
ing Colorado to 2 feet freeboard. . . 28,700 tons. 

Total weight of water removed to 
bring dock to 2 feet freeboard after 


docking. 15,200 tons. 

Total water pumped. 43,900 tons. 


Difference in favor of floating dock. . 60,000 tons. 

Or, in other words, the comparison, under the most favor¬ 
able circumstances to the dry dock, would indicate that the 
water pumped in the case of the floating structure would be 
about 42 per cent, of that from the stationary dock. 

Location .—The cost of a drydock depends upon the nature 
of the foundation. Good solid rock foundation is not obtain¬ 
able in all localities; and when, as is the case at the New 
York Navy Yard, a soft bottom underlaid by a water-bearing 
stratum of fine sand is encountered, or, as at Bermuda, the 
problem of founding on coral is presented, the building of a 
suitable drydock involves great expense. and much uncer¬ 
tainty. On the other hand, the floating dock requires for its 
operation, a depth of water considerably greater than the dry- 
dock, and, if the proposed site has not this depth of water 
naturally, expensive dredging operations must be allowed for 
in the estimates. If the water is silt-depositing the cost of 
maintaining the desired depth must also enter the final decision 
as a factor. 

It has been pointed out that there is an advantage in warp¬ 
ing a vessel into a floating dock lying parallel to the shore in a 
. strong current. While this is very probably a real advantage, 
it is in some cases more than offset by the saving in valuable 
frontage by the use of a drydock. Undoubtedly there are 
times, however, when, for one reason or another, it is desir¬ 
able to change the location of a yard, and, under such cir- 






FLOATING DRYDOCKS. 


161 


cumstances, the mobility of the floating' dock might save the 
cost of the entire plant. 

Safety. As regards the safety of the ship docked, the dry- 
dock has an advantage which at first glance appears to be 
of gi eat moment, but which on closer study of service condi¬ 
tions would seem to be reduced to a minimum in the latest 
types of floating docks. It is true that when a ship is safely 
seated in a drydock, there is small chance of accident from the 
structure itself. Indeed, if the dock is well founded, this risk 
may be regarded as limited to caisson accidents alone. A ves¬ 
sel on a floating dock, however, may be jeopardized in a num¬ 
ber of ways, such, for instance, as inherent weakness of the 
structure itself, injury to the dock by collision, careless hand¬ 
ling of valves, faulty moorings, etc. All these dangers have 
been the subject of careful study, and, in the latest designs, 
simplicity of operation and uniform strength with a large fac¬ 
tor of safety have been sought, and, judging by the recent tests 
of the floating dock at Algiers and the floating dock Detvey, 
have been attained to a very satisfying degree. 

Commercial ship owners seem to prefer the floating dock, on 
account of its greater flexibility, which enables it to lift a ship 
in a condition approaching that in which it rests in the water. 
If a ship with a sag in the keel is placed on a rigid floor, as in 
a drydock, it is deformed by the amount of the sag, and un¬ 
usual strains are induced ; while the flexibility of the floating 
dock would permit it to assume the shape of the keel, and, by 
proper manipulation of the valves, the ship can be given either 
a hog or a sag. The warship, on the other hand, because of its 
delicate structure, demands that a perfectly rigid base be pro¬ 
vided in docking. As an indication of the approach to this 
requirement attained in practice, it may be stated that the 
U. S. S. Colorado, 14,500 tons, 504 feet long, caused a maxi¬ 
mum deflection, in the length of the Dewey of ItV inches, 
while the shorter battleship Iozva, 11,400 tons, caused a maxi¬ 
mum deflection in the same dock of 4 inches. 

Besides those mentioned above, other considerations often 
enter into the choice of types, among which may be men- 


162 


FLOATING DRYDOCKS. 


tioned the strategic value of mobility, possibilities of protection 
from the attacks of an enemy, possibilities of expansion for fu¬ 
ture demand, and facilities for affording light and air. The 
strategic value of mobility has been ably discussed by Civil 
Engineer A. C. Cunningham, U. S. N., in an article entitled 
“The Movable Base,”* from which the following is quoted: 

“By placing a thoroughly developed military floating dock 
at each of our naval bases, we may in time of threatened danger 
double our available bases on the coast by towing the docks to 
various points of vantage, or in the last extremity, if forced 
to retreat up our rivers and bays, we may take our floating 
docks with us and establish movable bases that will the sooner 
enable us to again reach our coasts.” 

As the drydock is usually built in the foreshore of a pro¬ 
tected harbor, and as the structure proper is below the level 
of the ground, it is better protected from the fire of an enemy 
than the floating dock with high towers forming conspicuous, 
targets. A crippled ship would be safer in a drydock in such a 
case than in a floating dock, since the latter would not be able 
to submerge without endangering its charge. The floating 
dock, however, could be towed farther up the harbor, and 
anchored in a place of greater safety, and this might more than 
offset the advantage of the stationary dock. 

From a commercial standpoint, much might be said for the 
floating dock, because of the possibility of starting with a 
short dock designed so as to be fit for use as a section of a 
longer dock. If expansion of trade warrants, other sections 
may be added from time to time, and the capital invested in 
the plant can be kept at a figure more nearly proportional to 
the earning capacity. 

In working under a ship, light is a matter of necessity, and 
in masonry docks, especially those with small side-wall batter, 
this object is not always obtained in a satisfactory manner. 
Paint will not dry quickly or thoroughly in poorly ventilated 
places, nor are workmen thus situated satisfied or efficient. In 


* Proceedings of the Naval Institute, Vol. XXX, No. 1. 







FLOATING DRYDOCKS. 


163 

both these respects, the floating - dock has a great advantage. 
The drydock, however, has an equal advantage when it comes 
to handling material, heavy pieces of machinery, guns, etc. 
It is practically impossible to install traveling cranes of any 
considerable capacity on the narrow walls of a floating dock 
without interfering with the handling of the lines to such an 
extent as to render them undesirable. All material must come 
to a floating dock by bridge, wharf or float, and in neither case 
can the work be done as conveniently nor as economically as 
in the case of the drydock, where cranes of from 40 to 100 
tons capacity may encircle the excavation, and yard railways 
communicate with nearby shops. 

There is, however, one particular in which the floating dock 
has a most important advantage over stationary docks, from a 
naval point of view. A drydock can never dock a ship with 
a draught exceeding the greatest depth of water over the 
blocks, whereas a floating dock can be submerged to within a 
short distance of its side-wall decks. This advantage may be 
realized in comparing the Dewey, which can safely be given 
a depth of 37 feet over 4-foot keel blocks, while the side 
walls retain a freeboard of 4 feet, with the deepest naval dry- 
dock (Norfolk dock No. 3, under construction), which will 
have a maximum depth of 32 feet over the blocks. By dock¬ 
ing on 3-foot keel blocks the depth of water on the Dewey 
could be increased to 38 feet. In an emergency such as the 
accidental disabling of a ship so as to bring her down con¬ 
siderably by the bow or stern, this advantage of the floating 
dock might be the means of saving an investment of millions 
of dollars from total loss. 

In passing from this part of the discussion it may be worth 
while to draw attention to the fact that sewage can be easily 
and safely carried from a ship in a floating dock by pipes sus¬ 
pended beneath the ship’s scuppers and led overboard through 
the side walls. This arrangement enables the ship’s crew to be 
kept on board and under the supervision of officers, and adds 
greatly to favorable health conditions in tropical stations. 


164 


FLOATING DRYDOCKS 


Types of Steel Floating Docks .—Very complete reviews of 
floating-dock construction have recently appeared in the tech¬ 
nical press and the Transactions of various engineering socie¬ 
ties, among the most comprehensive of which may be men¬ 
tioned that contained in ‘'The Cavite Floating Dock”* by 
Civil Engineer A. C. Cunningham, U. S. N., and Mr. Clark’s 
paper on floating docks previously referred to. It could hardly 
add to the knowledge of the subject to attempt such a review 
in this paper, but it may help to a freer discussion if a brief 
description of the designs marking successive steps in the evo¬ 
lution of the modern floating dock be given. 

The earliest design consisted of a vessel of rounded form 
approximating the shape of a ship. This vessel was perma¬ 
nently closed at one end and fitted with a movable gate at 
the other, and was operated like an ordinary stationary dock. 
The gate dock gave way to the round-bottom dock, depending 
for its lifting power on the buoyancy of its interior compart¬ 
ments alone, and self-docked by careening. The old Bermuda 
dock is of this type, and is still in use. The solid-trough 
dock next appeared, and is still much favored for wooden 
structures of small capacity. Steel docks of this type are some¬ 
times built for fresh-water harbors, but when located in salt 
water there is usually included in the plant a shore basin for 
self-docking purposes. This type has many advantages in the 
way of strength, rigidity and low first cost, and, beyond a 
doubt, would be the ideal floating dock today if the lack of 
self-docking facilities could be remedied. Many devices have 
been proposed for getting at the under-water body of the solid 
dock, but, thus far, none has given sufficient promise of success 
to warrant adoption. A caisson arrangement for attachment 
to the bottom has been in use in Holland, but it is not known 
with what measure of success. The old Carthagena dock is 
an example of the solid-trough dock. 

Sectional Docks .—In order to permit of self-docking, the 
ordinary sectional dock was evolved. It consists of a number 
of solid-trough sections, of such length that one could dock 


* Journal of the American Society of Naval Engineers, Vol. XV, No. 2 . 



FLOATING DRYDOCKS. 


165 

another, as shown in outline in Fig. 1. The different sections 
were loosely connected by timber toggles, and the operation 
of docking required skill and careful attention, in order that 



Fig. 1. 

each section might take its own share of the load, and all lift 
in unison. Examples of this dock in timber are very common. 

Rennie Type .—The type designed by Mr. G. B. Rennie, one 
of the pioneers in floating-dock work, consisted of side walls 
in one piece, forming continuous girders for longitudinal 
strength, resting on a number of pontoons. This dock .could 
be self-docked by disconnecting a pontoon, turning it so that its 
breadth lay parallel to the axis of the dock, and hauling it over 
the pontoons remaining in position, as shown in Fig. 2. The 



_L__ _ |1 1[ _ 

Fig. 2. 

17,000-ton Bloom and Voss dock, at Hamburg, is an example 
of this type. Its chief objection consists in the fact that it is 
impracticable to place the pumps in the lowest position on 
account of the break between the side walls and the pontoons. 



































































FLOATING DRYDOCKS. 


166 

Clark and Standdeld Type {Havana ).—In this dock, Fig. 3, 
the side walls are in one piece, but, instead of resting on the 
pontoons, they extend to within a few feet of the full depth of 
the pontoons, and the latter lie between the former, and are 
connected thereto by joints made up of fish-plates and bolts. 
The number of pontoons is unlimited, and the operation of 
self-docking consists in disconnecting one pontoon at light 
draught, submerging the dock, bolting the loose pontoon to a 




Fig. 3. 



second-connection diaphragm higher up on the side wall than 
the regular connection, and pumping to the desired elevation 
in the regular manner. The side walls are docked by careen¬ 
ing. The Havana dock—now Dock No. 2 at the Pensacola 
Navy Yard—and the new dock at Algiers, La., built by the 
Maryland Steel Company, are examples of this type. The 
self-docking operation is entirely practicable, but tedious and 
rather complicated. The greatest drawback to this type of 
dock is the difficulty of making it sufficiently rigid to meet 
naval requirements, the expense of construction and the in¬ 
convenience of self-docking. During the acceptance tests of 
the Algiers dock the self-docking was successfully accomplished 
in 40 days, the pontoons being lifted 4 feet, and the side walls 
21 inches above the water. 



Clark and Standdeld Tola Type .—This dock, Fig. 4, is sec¬ 
tional, and each section is a solid trough with side walls and 
pontoons in one piece. The connections between the sections 
are made by bolts through flange angles which run around the 





























FLOATING DRYDOCKS. 


167 




Fig. 4. 


edges of the transverse faces. To make the joint watertight 
rubber gaskets are placed between the flanges. The method 
of disconnecting, as described by the inventor, consists in 
removing the upper bolts while the lower bolts remain in 
place; the outer ends of the pontoons are then water-ballasted, 
causing the sections to press together at the bottom, and thus 
enabling workmen to enter and remove the remaining bolts 
in the dry. For self-docking purposes, the side walls are 
cut away for a short distance on the bow and stern sections, 
and these portions of the pontoon deck are drawn under the 
third section, as shown in the sketch. It is claimed by the 
inventor that, as each section is built solid, and they are con¬ 
nected all around their contact edges, it is the strongest self¬ 
docking dock—a claim which probably held good at the time 
it was invented, though, in the matter of strength, it could 
hardly be compared with the Dewey, of later date. Whether 
or not the Pola Dock, the only one thus far constructed on this 
plan, has been self-docked is not now known, but it would 
certainly appear to be a difficult matter to keep the connection 
chambers free from water; and the removal of bolts might 
be attended with some danger. Holding the docked pontoon 
on the narrow ledge of deck available, would be out of the 
question in anything but perfectly still water, and, under the 
most favorable conditions, self-docking would require very 
skilful handling. 

The Cunningham Sectional Dock .—This dock, Fig. 5 > de- 
























FLOATING DRYDOCKS. 


168 


r 





Fig. 5. 


veloped and patented by Civil Engineer A. C. Cunningham, 
U. S. Navy, consists of solid-trough sections joined together by 
fish plates and bolts. The self-docking is effected by connect¬ 
ing two of the sections to the third by diaphragms, placed for 
the purpose at a higher elevation than those ordinarily used. 
This dock claims the advantage of having exactly similar ele¬ 
ments, thus permitting expansion at any time byHhe addition 
of sections. The connections can be made at any time by the 
addition of sections. The connections can be made of suffi¬ 
cient strength for naval requirements, and the self-docking 
operation is a very simple matter. This type should, and 
doubtless will, prove especially attractive for commercial 
purposes. 

Maryland Steel Company Type .—This type of dock, orig¬ 
inated and patented by Mr. Henrik F. Hansson, consists of 
a main pontoon of solid-trough section, with side walls ex¬ 
tending beyond its length and bearing directly on the decks 
of the two shorter end pontoons. The end pontoons have low 
independent side walls, to afford stability in self-docking opera¬ 
tions, and contain independent pumping plants. In self-dock¬ 
ing, the center pontoon takes both end pontoons on the blocks 
in the regular manner, and to dock the center pontoon 
the bow and stern pontoons are drawn under its ends, as shown 
in Fig. 6. This arrangement, with its long, solid main section. 



























FLOATING DRYDOCKS. 


169 


—E= 


D 



_ i—- .j juZIHr]- 

Fig. 6. 

gives nearly the strength and rigidity of the solid-trough dock, 
and is the simplest of all types in its self-docking operations. 

Design of a Floating Dock. 

Instead of discussing in general the principles governing 
the design of a floating dock, it is believed that the example of 
a dock actually constructed will prove of greater value in form¬ 
ing the basis for discussion of the subject, and, with this in 
view, a rather detailed account of the inception, design and 
construction of the U. S. floating dock Dewey, intended for 
the Philippine service, will be given. 

Choice of Dock .—In 1902, the date of the act authorizing 
the construction of the dock, the Philippines had been in the 
possession of the United States for five years, and the necessity 
of maintaining a fleet in Philippine waters had been recognized 
for some time. The old Spanish naval station at Cavite was 
badly located, and Congress hesitated to authorize further 
expenditure at this place until the question of a site for a per¬ 
manent station had been settled. The need for docking facil¬ 
ities in the Philippines was urgent, • as without them a voy¬ 
age to Hongkong, Kobe or Yokohama was a periodical neces¬ 
sity for every ship of the squadron. If a large investment were 
to be tied up in docking facilities, it was desirable to obtain 
a structure which could be moved, should future developments 
render such a step advisable. Again, the Department s ex- 















































FLOATING DRYDOCKS 


170 

perience with masonry drydocks established the fact that 
from 5 to 7 years are required for construction here at home, 
where labor conditions, prices of material, etc., are known, 
and the 18,000-ton floating dock at Algiers was constructed in 
27 months from the date of awarding the contract. These 
considerations alone would have been sufficient to have caused 
the adoption of the floating dock, but other features of the 
type were so happily adapted to the requirements of the case 
that no other decision could have been wisely reached. Not 
least among them was the fact that a floating dock could be 
equipped with a small machine shop, and, in a location where 
there are no shops, contain within itself an outfit for making 
all minor repairs. 

The Specification ,—The Bureau of Yards and Docks, in 
whose province lay the carrying out of the terms of the act, 
had just built the floating dock at Algiers, La., a structure 
which represented the highest progress then attained in dock 
building, and, with the idea of obtaining the very best re¬ 
sults, decided to leave the design to open competition under a 
general specification. This specification was drawn up by Civil 
Engineer A. C. Cunningham, U. S. Navy, whose experience as 
officer in charge of the Algiers dock gave him a peculiar fitness 
for the task. The result was a specification, acknowledged 
to be the most complete ever written for a structure of this kind. 
Paragraphs setting forth requirements, the knowledge of which 
is necessary to a complete understanding of the detailed design, 
are given herewith. 

Extracts from the Specification for the Cavite Self- 
Docking Steel Floating Drydock. 

“1. Intention .—It is the declared and acknowledged inten¬ 
tion and meaning to provide and secure a complete and sub¬ 
stantial self-docking floating steel drydock of American manu¬ 
facture suitable for docking all of the present and projected 
ships of the United States Navy, for which appropriations 
have been made, located and installed in complete and perfect 
working order, together with all moorings, wharves, ap- 



FLOATING DRYDOCKS. 


I?I 

proaches, accessories and appurtenances necessary for its per¬ 
fect, complete and convenient operation and maintenance, to 
the entire satisfaction of the Chief of Bureau of Yards and 
Docks. 

9 - Time of completion .—The dock proper shall be entirely 
completed and ready for test in every respect and particular 
within twenty-seven calendar months from the date of the 
contract. 

23. Plans and specification .—General plans in sufficient de¬ 
tail to give the Bureau a perfect understanding of the design 
of the dock, its method of operation, manipulation and con¬ 
struction, and of the character and distribution of all mate¬ 
rial, machinery and appliances shall be furnished by bidders. 
The general plans shall be accompanied by a specification, stress 
diagrams and calculations in further amplification of the de¬ 
sign and its capabilities, with full explanations of all operations 
and manipulations. The character and make of all machinery 
and appliances shall be described in the specification, and all 
other details necessary to enable the Bureau to arrive at a 
correct and perfect understanding of what is proposed. The 
contractor shall furnish the Bureau with tracings of all general 
plans. 

“24. Detail plans .—The contractor shall prepare detail plans 
in amplification of general plans showing all parts of the 
dock and its appliances. Triplicate blue prints of these plans 
shall be submitted to the officer in charge for examination and 
approval before any work is performed. Tracings of approved 
plans shall be furnished to the Bureau. Approval of detail 
plans shall be of a general nature and shall not relieve the con¬ 
tractor from errors, discrepancies, or omissions that may occur 
therein which shall be remedied or supplied whenever discov¬ 
ered or required. 

“qi .—The location of the dock is at the Naval Station, 
Cavite, P. I., at a site to be selected, but the Government re¬ 
serves the right to reasonably vary the location as may be 
to its best interests before the final acceptance of the dock. 
The contractor shall provide moorings, approaches and other 




172 


FLOATING DRYDOCKS. 


necessary accessories and appurtenances suitable for the loca¬ 
tion finally selected by the Government. 

“32. General description. —The dock in general shall be an 
open-hearth steel structure, so designed and arranged as to be 
readily self-docking without the aid of divers or auxiliary 
constructions. It shall be self-contained as to operating ma¬ 
chinery, and capable of being towed from place to place safely 
without auxiliary bracing. It shall be of the general type 
composed of water-tight side walls and body, or pontoons, with 

a general I-1 shaped cross sections, and divided into sufficient 

watertight compartments to give great stability, there being 
not less than 6 transversely. Simplicity and certainty of opera¬ 
tion and freedom from possible disablement in all operations 
should be given careful consideration by designers. 

“33. Length. —The dock shall be not less than 500 feet long 
over all, none of which length shall consist of bracketed 
platforms without lifting power. 

“34. Width .—The dock shall have a clear width between 
fenders of not less than 100 feet. 

“35. Height and draught. —The decks of side walls shall 
have not less than 8 feet of clear height above the water, with 
30 feet draught over 4-foot keel blocks. 

“36. Lifting capacity. —The dock shall have a lifting capac¬ 
ity of not less than 16,000 gross tons, uniformly distributed 
over its entire length, with the main deck not less than 2 feet 
above the water and with not less than 1 foot of water in the 
compartments. 

“ 37. Unit stress. —No portion of the dock, or its connections, 
shall have a stress of more than 10,000 pounds per square inch 
under the specified loads, or of 15,000 pounds per square inch 
in self-docking, with a wind pressure of 30 pounds per square 
foot of exposed surface. 

“38. Shiploads. —The dock shall be designed to dock all 
classes of vessels of the United States Navy, either centrally 
or with the center line of the keel 1 foot off the center line of 
the dock, with a freeboard of 2 feet, and shall provide for 
bearing over the full length of dock. Diagrams of weights,, 
as far as available, will be furnished on application. 





Deck House 

Coal Bunker x-BoIler .Engine -Coal Bunker^^Boiler 


Coal Bunker. 


Boiler 


Cajvstan[||] 


-pr-1. ItH. 


•flJdi hint-Shop* 


LMtilliug 
Plant __ 


Capstan^ 


'apetan 




Donkey Boiler-' 


Dynamo Blower CD 


Do* k y*tur 


Coal Bunker- 


PROPOSED SELF-DOCKING STEEL FLOATING DOCK OF 16,000 TONS CAPACITY 

FOR U. S. NAVAL STATION, CAVITE, P. I. 


-IG - 


r— t-t4980 ! 
SOI 0- 


30 


Starboard Sidewall 


Port Sidewall 


GENERAL ARRANGEMENT 


ci x —• Engine Blower 


Engine 


l*i_ 

[K.'iii c 


Face p. 172. 





































































































































































































































































































































































































































































































































FLOATING DRYDOCKS. 


x 73 


“39- Distribution of load .—The dock shall be so designed 
that the entire weight of a battle ship may be safely carried 
by the main keel blocks, or one-half the weight on each line 
of docking keel blocks, in whichever position the ship may be 
docked. The side walls shall be designed to take shoring at 
any point that may be necessary. 

“40. Working deck .—The working deck of the dock shall 
be flush-plated and so strengthened that docking keel blocks 
may be placed in any position. 

“41. Uniform pumping .—The dock shall be so designed 
that the specified unit stress shall not be exceeded when the 
dock is pumped uniformly from all compartments to a free¬ 
board of 2 feet with any specified shipload docked centrally. 

“42. Allozvable deflection .—With any specified shipload 
docked centrally and all compartments pumped uniformly until 
the dock has a freeboard of 2 feet, the longitudinal and lateral 
deflection over the entire working deck of the dock shall not 
exceed 1 in 2,000. Within the limits of allowed deflection the 
shipload shall be assumed to be perfectly flexible. 

“43. Keel blocks .—All keel blocks shall be of clear heart 
oak, of a uniform length of 5 feet, a width of 16 inches, and 
planed to a uniform thickness of 12 inches so as to be'inter¬ 
changeable. 

“44. Spacing of blocks .—Main keel blocks shall be spaced 2 
feet on centers and docking keel blocks 4 feet on centers. 

“45. Block sills .—Docking keel blocks shall rest on sills of 
clear heart long-leaf yellow pine, 16 inches wide and planed to 
a uniform thickness of 12 inches so as to be interchangeable. 
The sills shall be of sufficient length to accommodate all the 
docking keels in the Navy. 

“46. Sliding blocks .—Every third sill shall be fitted with a 
sliding block, and shall extend to within 2 feet of the mam 
blocking and sufficiently outboard so that the blocks cannot be 

hauled off the sill. 

u 47. Drainage. —Athwart-ship and fore-and-aft drainage 

shall be provided on the working deck of the dock. 

“48. Side wall decks .—The decks of side walls shall have a 



174 


FLOATING DRVDOCKS. 


clear passage fore and aft of not less than 5 feet in width. 
They shall have a hand rail on the outboard side and a 12 by 
16-inch clear heart yellow pine timber on the inside fitted with 
fair leads and cleats. 

“49. Passage. —Passage from one side wall to the other 
shall be provided. 

“50. Communication. —Telephone or speaking-tube commu¬ 
nication shall be provided from one side wall of the dock to 
the other, along the side walls, and to the engine rooms. 

“51. Headline .—Provision shall be made for a central head¬ 
line and for hauling the same from side walls. 

“52. Capstans , winches and bitts. —There shall be not less 
than four capstans on each side wall and the necessary capstans 
or winches for handling moorings. There shall be not less 
than eight bitts on each side wall. 

“53. Moorings. —Two sets of moorings shall be provided at 
each corner of the dock. 

“5.7. Runways and shoring stages. —Two lines of runway 
and shoring stages not less than 36 inches wide shall be pro¬ 
vided on the inner side of each side wall and a runway about 
2 feet above the main deck. 

“55. Ladders and steps. —Access shall be had to the run¬ 
ways and shoring stages bv suitable ladders and steps from the 
top of side walls and main deck. 

“56. Fenders. —All parts of the dock liable to be fouled by 
a ship in docking shall be fitted with heavy rubbing timbers 
and fenders, so arranged as to not injure the dock if carried 
away and to be readily replaceable. The exterior of the dock 
shall be fitted with fenders and rubbing timbers as a protection 
from drift and fouling. 

“57. Fire service. —A fire service and washing-down system 
shall be provided the entire length of each side wall at or 
near the top, and with not less than four hose connections on 
each side. 

“58. Indicator system .—The dock shall be fitted with a re¬ 
liable pneumatic or hydraulic indicator system to show the 
depth of water in all compartments at all times. 


FLOATING DRYDOCKS. 


175 


“59. Levels and gauges .—The dock shall be fitted with lev¬ 
els and gauge boards to indicate the trim. 

“60. Height of self-docking .—When self-docked, all under¬ 
water portions shall be raised to a clear height of not less than 
5 feet, and shall be safely and readily accessible for inspection, 
painting and repairs. 

“61. Self-docking connections. —With the dock at light- 
draught line, all self-docking and strain-transmission connec¬ 
tions shall be above water. 

“62. Pozver .—The dock shall be operated by steam power, 
and shall be fitted with all the necessary boilers, engines, pumps, 
feed-water heaters, steam separators and other accessories de¬ 
sirable to make a first-class self-contained plant. 

“63. Boilers and engines. —There shall be not less than 600 
nominal horsepower of boilers and engines suitably distributed 
to give the best results. Simplicity and certainty of action 
and freedom from possible breakdown in operation are to be 
given the first consideration. Engines of a type and style 
which will produce the least vibration in the side walls are 
desired. 

“64. Main pumps. —If of the centrifugal variety, the main 
pumps shall have a discharge of not less than 16 inches and 
an equivalent discharge for other varieties. 

“65. Piping. —All piping shall be of ample size to supply 
the pumps at maximum speed, and so installed as to be readily 

accessible for repairs or renewal. 

“66. Valves. —The piping and flow of water shall be com¬ 
pletely controlled by a system of simple and durable bronze- 
mounted valves, of the wedge variety, of easy and ceitain opei- 
ation. All valves shall be fitted with indicators. 

“67. Fuel arid water. —Storage shall be provided for fuel 
and fresh water sufficient for two complete successive dockings, 
of the maximum load. 

“68. Connections to ship. —Provisions shall be made for 
supplying a ship in dock with water and for cai rying off her 
waste water and sewage. 

“69. Machine shop. —A small machine shop, suitable for 
light repairs to the dock, shall be installed in one side wall. 





176 


FLOATING DRYDOCKS. 


“70. Storerooms and quarters. —Such portions of the side 
walls above the engine decks as are not occupied by machinery 
shall be fitted as storerooms, and as quarters for the dock’s offi¬ 
cers and crew, with suitable mess arrangements. 

“71. Hatches, skylights, deadlights and ladders. —The side 
walls shall be fitted with all the necessary hatches, skylights, 
deadlights, ladders and other conveniences necessary or desir¬ 
able. 

“72. Lighting plant. —An electric-light plant shall be in¬ 
stalled on the dock for lighting all interior working and stor¬ 
age compartments and with connections for portable lights on 
the dock. 

“73. Ventilating system. —A blower system shall be installed 
for ventilation of all working and storage spaces and quarters 
in the dock. 

“74. Time of operation. —The dock shall be designed to 
lift a load of 16,000 gross tons, with a draught of 30 feet 
clear of the water, in 4 hours. Lighter loads of less draught 
shall be lifted in a correspondingly shorter time, and the pumps 
shall readily operate under a head of 35 feet. The time of 
operation will be reckoned from when the ship has taken the 
blocks and shores and pumping is commenced until the keel 
is out of water. 

“75. Place of tests. —All docking and self-docking tests shall 
be made at a suitable and convenient place at or near the 
works of the contractor. 

“76. Preliminary tests. —Preliminary tests in sinking and 
raising the dock and in operating all machinery shall be made 
by the contractor to satisfy the officer in charge that the dock 
is in perfect working order. 

“77. Cruiser test. —The dock shall be tested in docking a 
cruiser furnished by the Government, centrally or off line, as 
specified. 

“ 7 ^- Battle-ship test. —The dock shall be tested in docking 
a battle ship furnished by the Government, centrally or off line 
as specified. 

“79. Deflections. —Observations shall be made for deflection 


FLOATING DRYDOCKS. 


177 


and permanent set during the dockings, with specially designed 
instruments furnished by the contractor, which will become 
part of the dock’s outfit. In determining the final deflection, 
allowance shall be made for permanent set and temperature de¬ 
flection, and the blocking shall be straight. 

80. Self-docking tests. —The dock shall be completely self- 
docked upon the completion of the docking tests. 

81. Board of tests. The tests shall be conducted by a 
board of naval officers, appointed by the Secretary of the Navy, 
one of whom shall be a line officer expert in steam engineering, 
one a naval constructor, and one a civil engineer. The dock 
will be carefully examined by the board and tested for all 
specified requirements. 

“82. Conduct of tests. —In docking naval vessels the ships 
shall be maneuvered, entered, and placed in position in the 
dock by the commanding officer and the naval constructor of 
the board, according to naval practice, with tugs and labor fur¬ 
nished by the contractor. All preparations and manipulations 
of the dock in testing shall be conducted by the contractor to 
the satisfaction of the board. A mutual understanding and 
agreement shall be had by the board and contractor preceding 
docking tests, to prevent accidents to the ship or dock. 

“83. Duration of battle-ship test. —On the last test the battle 
ship shall be carried centrally on the dock for 48 hours with¬ 
out the dock showing any undue signs of strain or fatigue. 

“84. Condition on delivery. —If the dock is delivered by the 
contractor at Cavite, all machinery, valves, strain-transmission 
and self-docking connections shall be put in perfect working 
order before the dock is turned over to the Government. 

“83. Docking material. —All the necessary material and ap¬ 
pliances needed in testing and operating the dock shall be 
supplied by the contractor and become part of the dock’s 
outfit. 

“86. Dock equipment. —The dock shall be provided with all 
conveniences for operation, manipulation and self-docking. 

“87. Boats. —Two 20-foot metallic lifeboats with complete 
•equipment shall be provided with the dock. 

12 




i?8 


FLOATING DRYDOCKS. 


Materials. 

“88. Quality. —All materials and workmanship shall be of 
the best quality of their respective kinds when the grade is not 
specifically mentioned, and the acceptance of same is under¬ 
stood and agreed to be subject to the approval of the officer 
in charge. 


Structural Steel and Iron. 

“89. —The steel for this work shall be made by the open- 
hearth process. 

“go. Structural steel. —Structural steel shall have a maxi¬ 
mum tensile strength of 55,000 to 65,000 pounds per square 
inch, an elastic limit of not less than one-half the maximum 
tensile strength, an elongation of not less than 23 per cent, in 8 
inches. It shall bend when cold 180 degrees around its thick¬ 
ness and when at or above a red heat 180 degrees flat, all 
without rupture on outside of bent portion. 

“91. Rivet steel. —Rivet steel shall have a maximum tensile 
strength of 47,000 to 55,000 pounds per square inch, an elastic 
limit of not less than one-half the maximum tensile strength, 
an elongation of not less than 25 per cent, in 8 inches. It 
shall bend when hot, cold or quenched *in water of 70° F. 180 
degrees flat, all without rupture on outside of bent portion. 

“92. Steel castings. —Steel castings, after annealing, shall 
haxe a maximum tensile strength of not less than 60,000 
pounds per square inch, an elongation of not less than 15 per 
cent, in 2 inches. They shall bend when cold 90 degrees 
around three times their thickness and when at or above a red 
heat 180 degrees flat, all without rupture on outside of bent 
portion. 

“93. Phosphorus and sulphur limits for steel. —Acid open- 
hearth steel shall not contain more than eight one-hundredths 
of 1 per cent, of phosphorus, and basic open-hearth not more 
than five-hundredths of 1 per cent. No steel shall contain 
more than five one-hundredths of 1 per cent, of sulphur. 


FLOATING DRYDOCKS. 


1 79 


“ 94 - Identification of steel.— All steel shall be stamped with 
its cast number. 

“95. Wrought iron .—Wrought iron shall be tough, ductile, 
fibrous and fiee from steel scrap. It shall have a maximum 
tensile strength of not less than 48,000 pounds per square 
inch, an elastic limit of not less than one-half the maximum 
tensile strength, an elongation of not less than 12 per cent, 
in 8 inches. It shall bend when cold 90 degrees around three 
times its thickness and when at or above a red heat 180 
degrees flat, all without rupture on outside of bent portion. 

u q 6. Iron castings .—Iron castings shall be made of the best 
quality of tough gray foundry iron and shall have a maximum 
tensile strength of not less than 18,000 pounds per square 
inch. 

“ 97 • Tests of iron and steel .—All tests shall be selected by 
a Government inspector. For steel there shall be not less than 
one of each kind for determining the physical and chemical 
qualities of each cast, and for iron a sufficient number to 
determine the quality of the lot under inspection. 

“98. Variations .—Rolled material shall not vary more than 
2 l /> per cent, from section or weight ordered, except in the 
case of wide sheared plates, where standard variations will be 
allowed; castings shall be true to drawings. 

“ 99 - Defects .—All rolled and cast material shall be free 
from defects and imperfections and true to section. 

“100. Inspection of steel and iron .—All steel and iron shall 
be tested and inspected by a Government inspector at the place 
of manufacture before shipment. Orders for steel and iron 
shall be marked ‘Inspection by Bureau of Yards and Docks, 
Navy Department,’ and triplicate copies shall be forwarded 
to the Bureau from the shop where the material is ordered in 
order that the inspection may be arranged, and one copy to 
the officer in charge for his information. Lists of material 
offered for inspection (with cast numbers in the case of steel) 
shall be furnished the inspector by the mill. 



i8o 


FLOATING DRYDOCKS. 


Workmanship. 

“ioi. General character. —All members and parts shall be 
manufactured and finished in a neat and workmanlike manner 
in accordance with best American ship practice, and to the 
satisfaction of the officer in charge. 

“ 102. Details and connections. —All details and connections 
shall be designed to develop the full strength of main members 
and for the greatest possible stiffness. The least number of 
parts consistent with the best results shall be employed in all 
details and connections. 

“joj. Accessibility. —All details and connections shall be 
readily accessible for inspection, painting and repairs. 

“104. Calking .—All watertight work shall be carefully ma¬ 
chine-calked as the work progresses and tested in detail as 
far as possible. The work shall be so designed that all calking 
edges are accessible in the finished dock. 

“105. Watertightness. —The completed dock shall be made 
perfectly watertight before acceptance so that it may be held 
in any position, light or submerged, without settlement. 

“106. Access to interior. —Easy access to all interior por¬ 
tions of the dock shall be provided. 

“ 107. Least thickness. —No material of less than Y inch in 
thickness shall be used in any portion of the dock which is 
subject to stress. 

“108. Pitch of rivets. —In watertight work the pitch of 
rivets shall be such as to insure perfect watertightness, but in 
no case shall it be less than three diameters, and in general 
not to exceed 6 inches. 

“109. Rivet holes .—Rivet holes shall be smoothly punched 
tV inch larger than the rivet to be used. When work is assem¬ 
bled the rivet holes shall so closely coincide that the hot rivet 
shall enter without drifting. Slight mismatching of holes 
shall be corrected by reaming, provided a perfect hole can be 
obtained and a correspondingly larger rivet is used. 

“no. Rivets .—Wherever practicable all rivets shall have 
button heads on both ends of an approved form, and a sufficient 



FLOATING DRYDOCKS. 


181 


length of shank to completely fill the holes and form perfect 
concentric heads. Rivets in decks and wherever else necessary 
shall be countersunk. 

“in. Driving rivets.— Rivets shall be carefully heated and 
machine-di iven wherever possible, in such manner as to com¬ 
pletely fill the holes and form perfect heads. 

“112. Defective rivets. —Loose, burnt or imperfect rivets 
shall be cut out and replaced with satisfactory ones. 

11 3 - Inspection of workmanship. —All workmanship, ma¬ 
chinery and appliances shall be inspected at the place 0|f 
manufacture by a Government inspector. 

Painting. 

“114. Cleaning metal. —Before painting, all metal shall be 
carefully cleaned of all loose scale, rust, grease, dirt, chips and 
other foreign matter by hammering, scraping and brushing 
with wire brushes. 

“ 115. Paint. —The paint in general shall consist of red lead, 
white zinc, japan dryer and raw linseed oil, mixed in propor¬ 
tions as directed, and applied in such manner and at such times 
as directed by the officer in charge. 

“116. Contact surfaces. —Contact surfaces shall each re¬ 
ceive one coat of paint before assembling. 

“117. Painting. —The entire clock shall receive three coats 
of paint before launching, and shall be touched up wherever 
necessary on the completion of the tests. In addition to the 
general painting, the engine rooms, boiler rooms and quarters 
shall be finished as directed in oil paint, ground cork, and 
cement floors. 

“118. Paint materials. —All paint materials shall be of ap¬ 
proved quality and delivered in original packages. 

Proposals. 

“ 119. Certified check and bond. —Each proposal must be ac¬ 
companied by a certified check, payable to the Chief of the 
Bureau of Yards and Docks, for the sum of $25,000, as a 






182 


FLOATING DRYDOCKS. 


guaranty that the bidder will execute the required contract 
within ten days after its delivery to him for that purpose, and 
give a bond (preferably that of a first-class security com¬ 
pany) in a penal sum equal to 20 per cent, of the contract price, 
conditioned upon the faithful performance of the contract. 
Checks of unsuccessful bidders will be returned immediately 
after the contract is awarded, and of the successful bidder 
upon the execution of the contract. 

“120. Form of proposals .—Proposals and all exhibits, alter¬ 
nate plans, letters of explanation, circulars, and all other papers 
(except the certified check) which it is desired to have con¬ 
sidered in connection therewith must be made in duplicate. 
Proposals shall be made upon the prescribed blanks furnished 
bidders, as follows: 

“Item 1 .—Price for dock and appurtenances delivered 
and moored at Cavite ready for operation, and the 
time required for such delivery. 

“Item 2 .—Price for dock, moorings and appurtenances 
delivered at the works of the contractor ready for 
towing, and insured by the contractor for delivery 
at Cavite. 

“Item 5.—Price for the dock, moorings and appurten¬ 
ances delivered at the works of the contractor ready 
for towing, and without insurance. 

“Item 4 .—Price for towing the dock from the works of 
the contractor and delivering and mooring at Cavite. 

“Item 5.—In case the bids on any of the above items 
exceed the appropriation available, an opportunity is 
given under this item to submit alternate proposals 
for completing the work within the appropriation. 

“121. Acceptance and rejection of proposals .—In giving 
great latitude in the design of the dock, both as to its general 
features and details, it is the desire of the Government to 
secure a structure that will fully meet the present and future 
needs of the naval service in a dock for the safe and conven 7 
ient docking of all naval vessels, and for safe and convenient 



FLOATING DRYDOCKS. 


183 

preservation and repair of itself; and the Government reserves 
the 1 lght to determine the relative merits of all the designs pre¬ 
sented, ii respective of the price bid, and to accept the design 
which most fully meets its requirements, and to award the con¬ 
tract upon any of the above items, to accept any bid, to waive 
any defects and informalities in the proposals, and to reject 
any or all bids. 

“122. Bidders ability .—Before he is awarded the contract 
any bidder may be required to show that he has the necessary 
facilities, experience and ability to perform the work in a satis¬ 
factory manner. 

“123. Amount of appropriation .—The appropriation now 
available is $1,225,000. 

"124. Information .—For any further information needed 
by intending bidders, application should be made to the Chief 
of the Bureau of Yards and Docks. 

“Navy Department, 

“Bureau of Yards and Docks, December, 1902.” 

A careful study of the designs submitted resulted in the 
award of the contract to the Maryland Steel Company, of 
Sparrow’s Point, Md. The dock proposed has already been 
described under the name “Maryland Steel Company Type,” 
patented by Henrik F. Hansson, and shown in outline sketch 
in Fig. 6. 

General Dimensions .—Paragraphs 33 to 36 of the general 
specification govern the length, clearance between side wallsj 
minimum draught of water over keel blocks, minimum free¬ 
board, and the lifting capacity. The type of dock adopted 
required no altar at the junction of the side wall and deck 
(which was necessary in the Algiers dock for the pontoon 
■connections), and valuable space was gained by omitting 
that objectionable feature. A side-wall width of 14 feet was 
assumed for strength, space and stability considerations. The 
width of the painting stages was taken at 3 feet, to the out¬ 
side of the fender, so that the over-all breadth of the dock 
would be 134 feet. 



184 


FLOATING DRYDOCKS. 


The skeleton structure of the dock is the result of the 
assumption that the local ship load is to be transmitted by 
the transverse members to the side walls, which, extending 
the full length of the dock, act as longitudinal girders. The 
ship rests directly upon keel blocks spaced at 2-foot centers, 
and sills for bilge blocks are spaced at 4-|foot centers. As 
it is desirable to have the load placed symmetrically as regards 
the transverse girders, the position of the bilge sills limits the 
advantageous girder spacing to 8 feet, since a 4-foot spacing 
would require too many, and for a 12-foot spacing the neces¬ 
sary strength could not be obtained. 

For preliminary calculations, the load curve of the new 
16,000-ton ships was assumed to be made up of a uniform load 
of 30 tons per linear foot over 50 feet of the keel length at 
each end, and 50 tons per linear foot for the remainder of its 
length. On this assumption, the loads on the transverse gir¬ 
ders, spaced at 8-foot centers, due to the ship, amount to 400 
tons. This load may be considered as applied equally at three 
points, two points or one point, according as the ship is 
assumed to be supported by keel and bilge blocks equally, the 
two rows of bilge blocks, or by keel blocks only. The nega¬ 
tive loading due to the buoyancy amounts to: 

' I 6 )QC)Q X 8 X = 202 tons, uniformly distributed. 

500 J 34 

The transverse girders are fixed at the ends to the side walls: 
but, on account of the deformity of the structure as a whole, 
under stress, the span is taken from the centers of the side 
walls, or at 120 feet, and the girder is considered as simply 
supported; therefore: 

The maximum bending moment, ship resting 

on three blocks, is. 5.682 ft-tons- 

The maximum bending moment, ship resting 

on two blocks, is. 4,216 ft-tons. 

The maximum bending moment, ship resting 

on one block, is. 8,616 ft-tons. 






FLOATING DRYDOCKS. 


185, 

from which, using the specified unit stress of 4.46 tons per 
square inch, the moment of resistance required is 15,290 inch- 
thirds for the first case, 11,340 for the second and 23,184 for 
the third. As the case of a large ship supported by the keel 
blocks alone would be impossible in actual practice, the re¬ 
quired resistance moment in the first case above caused the ten¬ 
tative adoption of 18 feet as the depth of the pontoons. This, 
however, was increased to 18 feet 6 inches as a result of later 
and more detailed calculations. 

Assuming the weight of the dock and machinery to be 
11,000 tons, the weight of the dock and the ship is 27,000 
tons, to which must be added the weight of 12 inches of con¬ 
tained water, as provided in the specification, making a total 
of 28,900 tons when the specified ship is raised to 2 feet free¬ 
board. The displacement of the pontoons per foot may be 
taken at 1,900 tons. The depth of pontoons, less the 2 feet 



Fig. 7. 


specified freeboard, is 16.5 feet, which at 1,900 tons per foot 
gives a buoyancy of 31,350 tons, an ample margin above re¬ 
quirements. 

To obtain the required moment of inertia of the dock section 
as a whole, the bending moment at the center is obtained (Fig. 
7) as 345,000 ft-tons; from which the moment of resistance 
is found to be 928,250 inch-thirds. As it was found imprac¬ 
ticable to obtain this resistance with the limiting side-wall re- 



























186 


FLOATING DRYDOCKS. 


quirements set forth in Paragraph 35 of the specifications, and 
for the further purpose of insuring rigidity, the side-wall 
freeboard was increased 3 feet 6 inches, making the total depth 
of the side walls 36 feet 6 inches. 

The width of the independent side walls was taken at 8 feet, 
and increased to 10 feet on the ends to provide working room 
for operating the independent pumping plant. 

Hull Details. 

Skin Plating .—The displacement per foot, based on the 
above general dimensions, is 1,900 tons for the pontoons and 
side walls to the level of the main deck. The displacement per 
foot of both side walls is 380 tons. When the dock is at its 
maximum submergence (34 feet of water over deck) the dis¬ 
placement would be 48,480 tons, assuming that the independ¬ 
ent side walls, except engine rooms, admit of a free flow of 
water. Taking the weight of the dock at 11,400 tons, and 
assuming that 12 inches of air remain in the pontoons, the 
water in the side walls will rise to 9 feet above the deck, or 
25 feet below the water line. If no air is assumed to be left 
in the pontoon, the water will rise to 5.1 feet in the side walls 
leaving 28.9 feet head on the side-wall plating—a maximum 
head for side-wall plating. The maximum head on the bottom 
plating occurs when 12 inches of air is considered as remain¬ 
ing under the deck, and amounts to 35 feet. 

All attempts to derive a rational formula for the stress in 
flat plates have resulted in complicated expressions too cum¬ 
bersome for practical use, and the paucity of experimental data 
on plates of the size commonly used and under conditions 
approaching actual service has, so far, prevented the discov¬ 
ery of a satisfactory empirical formula. About all that is 
definitely known on the subject, at present, is that rectangular 
plates attached to frame angles by good riveting are subjected 
to a bending stress up to a certain point, after which the char¬ 
acter of the stress changes to something like that which obtains 
in a loaded chain. 








FLOATING DRYDOCKS. 


187 


Experience in the use of plates under water loading would 
indicate that there is little danger of actual failure under a 
static loading due to the range of heads with which the de¬ 
signer has to do, and that the methods used in current practice 
afford an ample margin to cover all dynamic loading. It is 
here suggested that if ship builders would adopt a maximum 
permissible deflection, expressed as a percentage of the short¬ 
est dimension of the unsupported rectangle of the skin plating, 
a satisfactory empirical formula might be derived from experi¬ 
ments on full-sized units, to which an impact factor could be 
added to provide for wave effect. Such a formula, if generally 
adopted, would not change present practice further than to 
provide uniformity of method. 

To determine the thickness of the skin plating on the Dezuey 
an elementary beam, 1 inch in width, was considered as fixed 
at the ends and supported at the edges of frame angles. If 
K represents the allowed intensity of stress, H, the head of 
water, in feet, and /, the span, the expression for the thick¬ 
ness may be written: 

H l 2 

f — O.OOOI — 

A 

Using the dimensions shown in Fig. 8 for a beam 1 inch 
wide, having a thickness, t; and a span of 21 inches, under a 
35-foot head of water: 

Then, t — 0.586 in. = if in. 



This method does not take into account the metal lost by 
punching, nor does it seem to be rational to take the span as 
the distance between the edges of the supports, because any 











188 


FLOATING DRYDOCKS. 


deformation of the flanges will destroy the usefulness of the 
flexure formulas. 

Experiments on full-sized plates, which were conducted 
during the construction of the dock (the results of which may 
be submitted to the profession at a later date), would indicate 
that the actual deflection is from one-third to one-fifth of that 
obtained by the fixed-beam formula, and that a considerable 
excess of strength is obtained by its use. It should be stated 
that these experiments were on plates supported only at their 
edges and not continuous over the supports. Therefore, they 
do not show the effect of continuity, nor do they indicate the 
effect of the ship’s distortion as a whole. 



(а) Fixed beam formula, Span 21* rivets, 6“Spacing deducted (%* gross hole) 

(б) ” . ” ” ” ” ” ” o ” ” ” (net rivet area) 

(c) Rectangular plate formula. K — lVCl*b~ -4- 2 t~ (a 4 -i- &*) 

(d) “ “ ' “ Bach, t 2 = 0.408 K (a 2 + 6 2 ) 

(<?) Fixed-beam formula, Span 2l“ no rivets deducted. 

(/) Experimental,- deflection== }/^ Span 

Fig. 9. 

Fig. 9 shows the curve of thickness required for different 
heads, as obtained by the fixed-beam formula, Bach’s formula 
for rectangular plates, and other well-known formulas. As a 
























FLOATING DRYDOCKS. 


189 


matter of interest, a curve is added showing 1 the thickness ob¬ 
tained by limiting the deflection to ^ of the span, as deter¬ 
mined by the experiments referred to above. 

If the lap is considered as a beam supporting two edges of 
a rectangular section of plating, a slightly less degree of 
thickness is required by the use of Bach’s formula. Taking 
the lap at 2p2 inches in width, and deducting rivet holes, it is 
found to be amply strong, with iVinch metal, to support its 
proportion of the load, but as the lap must suffer some distor¬ 
tion it would be hard to say- just what dependence could be 
placed upon it. 

Transverse Bulkheads .—The maximum bending moment to 



-Width Flange 96 
-Strake 40-- 


■jB x tt"x4F;x^L" 


-V 

28”x %*PI. 




TRANSVERSE BULKHEAD 

Fig. 10. 

which the transverse girders are subjected is 5,690 ft-tons, as 
obtained above. The plating required for the static head is 
inch, and the bulkheads are spaced at 8-foot centers. As the 
longitudinal frames keep the deck plating rigidly connected as 
a whole, the entire 96-inch section pf skin plating may be con¬ 
sidered as forming part of the girder flanges. This width will 























190 


FLOATING DRYDOCKS. 


include part of three transverse strakes, and the weakest sec¬ 
tion will occur at the butt of one strake. The butts are assumed 
as double-riveted in the center with rivets of 3-inch pitch, and 
one strake may be taken at about 40 inches, or as including 
about 22 rivets. Assuming the girder section shown in Fig. 
10, then, allowing only the rivet equivalent for the area of 
the middle strake, and making a proper reduction for rivet 
holes in the angles, gives a moment of resistance of 15,220 
inch-fourths, as against 15,290 required with the allowed 
unit stress of 10,000 pounds per square inch. At ir feet on 
each side of the center it* is desired to cut a central 15 by 
30-inch limber hole; and, at a distance of 17 feet, two such 
holes are needed. The reduced moments of resistance at those 
points are found to be amply large for the corresponding load 
moments. The transverse bulkheads are continuous between 
the side-wall bulkheads, and they are stiffened by the longi¬ 
tudinal frames besides the center and intermediate longitudinal 
bulkheads. 

To determine the deflection of the transverse bulkheads, the 
general equations for deflection are used. 

Moment between 0 and A, M (O — A)=Rx, 

Moment between A and B, M (A — B)= R x-\p(x — a) 2 
Moment between B and C,M (B — C)—Rx-\-% p(x — a) 2 


— IV (x—b). 
d 2 w 

Equating each of these expressions to E I j integrating, 


and noting the conditions when a, b. and d are substituted for 
x, the values of the constants are determined, and an expres¬ 
sion for the maximum deflection is obtained. Substituting the 
proper load and span values in the deflection expression, the 
theoretical maximum deflection of the transverse bulkheads 
under the maximum loading is found to be .0.56 inch, which is 
well inside the specified deflection of 1 in 2,000 (0.636 inch). 

Longitudinal Frames .—A frame spacing of 24 inches was 
adopted on account of the low unit stresses allowed and the 
extreme rigidity required. On the assumption that the ship 
rests on the bilge blocks alone, the direct load on each block 





FLOATING DRYDOCKS. 


igr 


placed 4 feet apart would be ioo tons. As the bilge blocks 
were specified to be 5 feet in length and were to rest on 12 
by 16-inch yellow pine sills, the loading may be considered as 
distributed between four longitudinal frames, making a direct 
concentrated load of 25 tons to each frame. Using the fixed- 


a 


R 


J 

A 

r 1 

r 1 

> 

r 

f 

b - > 

> 

<— c— > 

- 

f'4 + + t t t ttttttff 


Uniform Load of jj tons per inch. 


Fig. 11. 


R 


beam formula for concentrated loading, and taking the span as 
the distance between the centers of the rivet groups connecting 
the top member to the gussets, gives a required moment of 
resistance of 

/ 25 X 6 X 12 

8 X 4.46 “ 5 °' 4 ' 

Using a 15-inch by 33-pound channel for the top chord of 
the frames, and regarding the effective section of the plating 
above it as a part of the beam, gives a section composed of 
the channel, and a 24 by if-inch cover plate the area value of 
which is found by dividing the value of seven ^4-inch rivets 
for single shear by the allowed intensity of stress. This gives 
a moment of resistance of 48.7. To make up for the uncer¬ 
tainty as to the ends, and to insure rigidity, two knee-braces, 
composed of one 4 j 4 by 3 by iVinch angle, are added. 

The bottoms of the frames sustain the maximum water pres¬ 
sure only, and, by the use of knee-braces, the span may be 
broken up into three sections, the longest of which may be 
taken at 28 inches. Regarding each span as a series of fixed- 
end beams, non-continuous over the braces, gives for the re¬ 
quired resistance moment with a 35-foot head of water: 

~- = \— X 2 x4>- t 2X 4-46 — 4- 
d L 35 12 28J 














FLOATING DRYDOCKS. 


T 92 


Using a 6 by 3^4 by iVinch angle, and considering the 
rivet equivalent of a 24-inch strip of plating, gives a section 
having a moment of resistance of 4.2. 

The knee-braces carry the reactions from two 28-inch and 

H 2 

one 18-inch span, or, 23 X — X —= 3.8 tons. The braces 

3 .S 

are set at 45°, and are about 48 inches long, therefore the 
resultant stress is 5.4 tons. Using a 4J 4 by 3 by iVinch angle, 

with an ^ of 12, and a factor of safety of 4, the safe strength 

would be 3.5 tons per square inch—a total of 11 tons. The 
end spans of the bottom member would be subjected to a 
thrust, in addition to the bending, but as in that case the gross 
sectional area could be depended upon, its capacity is ample. 
The side angles of the frames are required to transmit the 
total upward thrust of the water to the transverse bulkheads, 




Fig. 12. 


and a 6 by 3^2 by iVinch angle, having a capacity for 50 
tons, is used, and is attached to the bulkhead by %-inch rivets 
spaced 6 inches apart. 

The end frames of the pontoons are provided with vertical 




































FLOATING DRYDOCKS. 


J 93 


plate stiffeners, calculated in the usual way to withstand the 
greatest unbalanced water pressure to which they are exposed. 
The top chords of the last five frames next the side walls are 
reduced in size to 12-inch by 25-pound channels, as they lie 
beyond the direct ship loads. 

Side-Wall Frames.—As the side walls form the main longi¬ 
tudinal girders, the framing serves mainly as spreaders, and 
are placed athwartships, instead of fore and aft. At intervals 
of 8 feet, and abutting the pontoon transverse bulkheads, is a 
braced frame for the purpose of transmitting the pontoon loads. 
Between the braced frames, and spaced 2 feet apart, are the 
ordinary box frames stiffened by knee braces and struts. The 
ordinary side-wall frames are calculated in the same manner 
as the pontoon frames, with the exception that their members 
are subjected to an upward thrust as well as to direct bending. 

The condition of loading for the braced frames is shown in 
Fig. 13* The buoyancy of the dock beyond the ship load is 


XXX 

— ■ 

50 Tons 

I 

X 

r v*~ 

A 

0 

w < 

a' 

0 

H 

s. 



Fig. 13. 


the supporting force, and must be transmitted through the 
side walls, acting as girders, to the ends of transverse girders. 
The braces carry this supporting force of 100 tons from the 
side-wall skin to the connections. Assuming that 100 tons is 
divided between the verticals, and that each of the six braces 
takes equal proportions, the vertical component of the brace 
stress is 8.3 tons, and the resultant brace stress is: 


For the top pair. 10.5 tons. 

For the middle pair. 13 tons. 

For the lower pair. 11.3 tons. 


A 5 by 5 by J 4 -inch angle is adopted, having a safe capacity 
for 18 tons. The connection between the transverse girder 
13 



















194 


FLOATING DRYDOCKS. 


and the side walls is calculated to withstand the shear and 
bending moment at that point. 

Longitudinal Girders .—The central longitudinal bulkhead is 
intercostal between the transverse 
girders, and, together with Frame 
No. i on each side, forms a com¬ 
pound girder receiving the direct 
loading from the keel blocks. The 
span is 8 feet, and the girder is 
strengthened by an intermediate 
breathing-plate extending from the 
center to Frame No. 2 on each side. 

The keel blocks are 5 feet long, and 
the ship load is regarded as dis¬ 
tributed over that space. Considering 
the ship as supported on keel blocks 
alone, the load per span of 8 feet is 
400 tons, to be carried between trans¬ 
verse girders. The section of girder 
adopted and sketch plan showing the area of rivets counted is 
shown in Fig. 14. 

The resistance moment of the section is ample, of course,, 
for the bending. To transmit the direct load into the girder,, 
the rivets are distributed as follows: 



Double 

shear. 

Equivalent 
single shear. 

Center bulkhead . 

29 

46 

Transverse bulkhead . . . . 

l6 

26 

Breathing plate . 

IO 

l6 

Two brackets. 



Four curtain plates. 


. 52 

Total single shear . . 




400-f- 160 = 2.5 tons per rivet in single shear, or 12,800' 
pounds per square inch. 

This result is deemed satisfactory when it is considered that 


-5-ft- 


Ktel Block 


00 s v/n P'- 


ll “RT 


1 • 9 

Vfe l 

' 4 Vj* x 4 x L 
ao*x vU pi. 


Web 220 x.yi« PI. 


-It- 


CENTER LONGITUDINAL BULKHEAD 


Fig. 14. 



















FLOATING DRYDOCKS. 


195 


the assumption that the whole ship rests on the keel blocks 
alone is one which can never materialize. 

The side and intermediate longitudinal bulkheads are made 
up, like the center, of iVinch plate and 4 >d by 4^ by ^-inch 



Curt: 

11 

in PI. 
entiling 
Urack 



CO 

p 

r2 

33 

ca 

T.B.H. 

T.B.H. 

SJ 



i- 

- 









- — 


p - 

— 


-1 


lid 

1 


i 

l 

1 

1 

I 

I 

1 

1 

| 


f 

I Cnii.L 

1 

1 

1 


1 

1 


1 

1 

1 

1 

1 



-r 

*1“ 

n—-— 

— 

- - 


- 




- 


- - 



- 

— 




• 










Rivets counted in area between dotted lines. 


Fig. 15. 

angles. The intermediates are strengthened by a channel rib 
placed horizontally at about one-third the depth to provide for 
unequal water pressure when listing the dock. 

Other Hull Details .—All non-watertight bulkheads have 12 
by 3 0_ i nc b opening's, to allow the passage of water, and are 
provided with small limber holes near the top and bottom 
flanges for air drainage. 

All connection details are computed in the regular manner, 
care being taken to avoid direct pull on the rivet heads. 

The bending moment at the joint between the pontoons, for 
both ship and dock loads, may be taken at 120,000 ft-tons. A 
section resistance moment of 323,000 is therefore required. 



Using the connections shown in Fig. 16, consisting of seven 
elements each comprising forty-four 2-inch bolts, and con¬ 
sidering the overhang with bolts alone, a resistance moment 

























































196 


FLOATING DRYDOCKS. 


of 730,000 inch-thirds is obtained. Using the overhang sec¬ 
tion and the section of the J4~inch diaphragm plate, a moment 
of 613,400 inch-thirds gives nearly twice the required strength. 
In addition to the vertical connections, a row of ij 4 -inch bolts 
connects the end pontoon decks with the four bottom edges of 
the overhangs, and there are 96 bolts in each row. 

The strength of the overhang section when unsupported by 
the end pontoon may be determined by the following assumed 
weights and their location: 

Weight of overhang. 320 tons, arm 40 feet. 

Weight of quarters. 10 tons, arm 44 feet. 

Weight of bridge. 8 tons, arm 80 feet. 

Weight of live load. 20 tons, arm 40 feet. 

Moment = 14,724 ft-tons, which, divided by the resistance, 
102,346, gives 1.16 tons per square inch stress. 



Fig. 17. 


Strength of the Dock as a Whole .—The moment of inertia 
of the dock, according to the above preliminary design, was 
taken at different sections as follows: 


Center 


384,681,832 inch-fourths. 


(a) 31.5 ft. from center.. 379,382,072 inch-fourths. 

(b) 39.6 ft. from center.. 371,764,400 inch-fourths. 

( c ) 49-5 from center.. 370,011,050 inch-fourths. 

(d) 56.25 ft. from center.. 368,218,500 inch-fourths. 

(<?) 70. ft. from center.. 348,510,714 inch-fourths. 

(/) no. ft. from center. . .321,140,084 inch-fourths. 

(g) 131.17 ft. from center..313,661,487 inch-fourths. 

(The center of gravity of the center section is 371.2 inches 
from the center o,f the bottom plating.) 




















Fig. 2.— U. S. S. “Iowa” Centered in Dock; Ready to Begin Pumping. 


Face p. 196 

























































FLOATING DRYDOCKS. 


197 


A second bending-moment diagram was then drawn, using 
the actual load curve of a 16,000-ton battleship. A compari¬ 
son of the required resistance with that provided above led 
to the doubling of certain of the tower-deck plates, the addition 
of a channel stringer and a slight increase in the thickness of 
the upper side-wall plating. The final moments of inertia 
corresponding to the above sections are as follows: 


At center 
Section a 
Section b 
Section c 
Section d 
Section e 
Section f 
Section g 


384,681,832 

379,382,072 

375,872,940 

374,188,880 

372,456,168 

353,061,010 

326,317,300 

322,667,487 


A curve was then drawn, with ordinates obtained by divid¬ 
ing the bending moment at various sections by the correspond- 

ing moment of inertia. Treating this curve, called the - j. - 

curve, as a load curve, the bending moment obtained from it 
indicates the deflection of the dock. The calculation was made 
graphically, and resulted in a maximum estimated deflection of 
2.9 inches at the center, slightly less than 3 inches allowed by 
the specification. 

In investigations of the dock’s strength on the crest or in 
the hollow of a wave of height equal to one-twentieth of the 
span, no bending* moment can be obtained exceeding 200,000 
ft-tons, which is small in comparison with that given by the 
ship. In self-docking the center pontoon, each end rests on an 
8o-foot deck length of end pontoon, and considering the dock 
as a beam of span equal to the distance between the center of 
bearings, a bending moment of 231,000 ft-tons is obtained. 
This, however, is on the assumption that the weight of the 
center pontoon, 7,750 tons, is distributed over the span, a moie 
severe condition than that which actually occurs as the o\ei- 
hangs tend to reduce the moment. 











98 


FLOATING DRYDOCKS. 


Stability. 


Referring to Fig. 18: 



PQST is a floating vessel; 

pqst is an interior compartment, partly filled with water; 
WL and W'U are water lines, before and after inclination; 
wl and w'l' are interior water surfaces, before and after in¬ 
clination ; 

B and B' are centers o ( f buoyancy, before and after inclina¬ 
tion ; 

b and b' are centers of gravity of interior water carenes, 
before and after inclination; 

D is the displacement of the dock, in tons; 
d is the weight of the contained water, in tons; 

V is the value of the displacement of the dock, in cubic feet 

= 35 d ; 

v is the value of the contained water, in cubic feet = 35 d; 

I is the transverse moment of inertia of the water planes; 
i is the transverse moment of inertia of the contained water 
surface. 

The metacentric radius, called R, is the distance, B Ad ; and 














FLOATING DRYDOCKS. 


199 


the metacentric height, called H, is the distance, G M = R — 
B G } or R — A. By a simple process, it is easily proven that 

R — ^>5 when I is the transverse moment of inertia of the 

water plane and V is the volume of displacement. The same 
expression can be used for the water in a contained compart¬ 
ment of a floating body, in which case the center of buoyancy 
and the centef of gravity are identical. 

When a vessel rolls, the contained water moves from side 
to side and acts in all respects as if it were suspended from a 
point which corresponds with the metacenter, m, of an empty 
vessel. The effect of the contained water, therefore, may be 
said to raise the center of gravity a distance, b m, in Fig. 18, 
which would raise the center of gravity of the whole vessel a 
distance 

~ d X b m 
GG = z? -> 


in which d = the weight of the contained water, in tons; and 
D = the displacement of the dock, in tons. Assuming 35 
cubic feet of sea water = 1 ton, 


D — — , and d — —» 

35 35 


therefore, 


_ v X b m 
G G =-p—» 



But, considering the interior compartment as an exterior 
carene, 


b m 



therefore, 


G G’ — lx - 
V v 




The moment of stability, therefore, is, 




200 


FLOATING DRYDOCKS. 


D . G' M sin. Q = D (G M — G G') sin. 6 

= d(g M— y\ sin. d, 

D . G' M == sin. 0 = new stability moment = M' 

= — sin. 0 , ... (3) 

Therefore the effect of the contained water is to reduce the 

2 2 

metacentric height by or 2 —should there be more than 
one compartment 


B M — R 


I 

V 

I 


H= R — A =j / —A 

H - 1 V=H' = I l ~A- i v 


H' 


I— A V 


V 


. . . . (4) 


Or, when there are more than one of such interior compart¬ 
ments, 

I — A V— li 


H' = 

From Equation 3, 


M f = D . H' sin. 6 = — . 

35 V 

M'= -^iI(/—A V—Zi), 


V 


V II —A V— h 


V 


j sin. 0 . 


35 

For 6 = i°, 


( 5 ) 


M' = 


I—A V— I i 


X 0.0175, 


( 6 ) 


The stability curves shown in Fig. 19 are constructed on 
Equations 4, 5 and 6. When the ship is on the dock its own 
stability must be taken into consideration, and the I of the 
above expression becomes I -f- I ± . 











Fig. 1. —U. S S. “Iowa” in Dock, with Pontoon Deck of Dock Awash. 



Face p. 200 




















FLOATING DRYDOCKS. 


201 


It will be seen from an inspection of Fig. 19 that there 
ci 1 tical points at the pontoon-deck level and at the top of 
blocking before the water plane cuts the ship. 



/ 


are 

the 











































202 


FLOATING DRYDOCKS. 


In determining the heeling effect of wind pressure, the 
moment of the wind, taken at 30 pounds per square foot over 
one side wall into the distance between the line of its action 
and the intersection of new and old water lines, is equated to 
the righting moment and solved for the angle of inclination. 

Calculations for stability were made for the following posi¬ 
tions : When the dock has a freeboard of 2 feet 6 inches; 
when the deck is flush with the surface of the water; and at 
points where the draughts are 4 feet, 17 feet and 30 feet 6 
inches above the deck. The curves shown on Fig. 19 are based 
on these calculations, and give the righting properties of the 
dock, with the lifted ship, at all positions. Similar curves were 
also drawn for the dock as a whole and for each section alone, 
with and without ship loading, and for self-docking operations. 

Machinery. 

The specifications require the dock to lift a 16,000-ton bat¬ 
tleship to a freeboard of 2 feet in 4 hours. The quantity of 
water to be removed is 34,700 tons in 4 hours. Three main 
pumping elements were decided upon, all of which were to be 
placed on the port side. The pumps were to be of the vertical- 
shaft centrifugal type, and to rest directly upon a main drain 
running throughout the length of the’side wall, with branches 
to each pumping compartment. Each pump, therefore, was 
required to lift 1,686 cubic feet of water per minute against 
a 35-foot head. Assuming a velocity of 10 feet per second, 
the area of the main drain required would be 2.8 square feet; 
therefore a 24-inch pipe was used, giving a velocity of 9 feet 
per second. The dimensions of the pumps for the preliminary 
design, with a maximum head of 40 feet, were determined as 
follows: 

Outside diameter of wheel. 4 feet 10 inches. 

Inside diameter of wheel. 2 feet 3 inches. 

Revolutions per minute. 225. 

Diameter of suction and discharge 24 inches. 

Engines .—The theoretic power required with a head of 40 
feet would be 130 H.P., and, assuming a hydraulic efficiency 





FLOATING DRYDOCKS. 


203 


of 58%, the actual engine power to be provided for each of 
the three pumping elements would be 225 H.P. Horizontal 
compound, non-condensing engines, 1414 by 25 by 14 inches, 
with cylinders set at an angle of 135 0 , were adopted. The 
angle between the cylinders gives a slightly unbalanced turn¬ 
ing moment on the shaft, but the disadvantage is of small ac¬ 
count, and, by placing the engines as nearly as possible in the 
direction of the length of the dock, vibration was reduced to 
a minimum, i he pumps and engines were designed and manu¬ 
factured by the Morris Machine Works, of Baldwinsville, 
N. Y. 

Boilers .—Babcock & Wilcox, marine-type, water-tube boil¬ 
ers were adopted, each of 1,750 square feet heating surface, 
46 square feet grate surface, and were designed to work at 
150 pounds steam pressure. 

Auxiliary Machinery .—An air compressor having a capacity 
of 527 cubic feet per minute was installed on the port side. 
On the starboard side was installed a small machine shop, 
with lathe, drill, shaper, etc., an electric generating set for 
lighting the dock, and an evaporator, fire pump, etc., together 
with a donkey boiler for generating* the necessary steam. 

Construction. 

The dock was constructed by the Maryland Steel Company, 
at its works at Sparrow’s Point, Md. A basin was excavated 
in the foreshore and closed by a coffer-dam. A sufficient num¬ 
ber of spruce piles were driven to support the estimated weight 
of the dock, allowing 6 tons to the pile. A 6-inch centrifugal- 
pump, electrically driven, was operated continually for drain¬ 
age. The structural material was rolled at the works of the 
Pennsylvania Steel Company, at Steelton, Pa., and of the Cen¬ 
tral Iron and Steel Company, at Harrisburg, Pa., and was 
milled at Sparrow’s Point. As the dock was designed to avoid 
all curved work, and as the type of structure renders possible 
the use of similar members, the multiple punch was available in 
machining all the plating and bulkheads, while all frames were 
assembled and riveted by yoke machines in the yard. 



204 


FLOATING DRYDOCKS. 


Erection was carried on in a simple and rapid manner. A 
trestle was built out into the basin at the same level as the pon¬ 
toon decks. Two io-ton traveling cranes, with arm height and 
reach sufficient to handle weights at any part of the completed 
structure, were erected on these trestles. As the first bay of 
the end pontoon was erected, the trestle stringers with crane 
tracks were extended over the transverse bulkheads. As the 
work progressed, the track was extended throughout the 
length of the dock. 

All detailed plans were prepared in the course o,f construc¬ 
tion, and, as the supervising engineer was permanently sta¬ 
tioned at the works, all plans were checked and approved with 
the least possible delay. 

The selection of a protective coating for the dock was made 
the subject of careful study. Samples of a number of the best 
known paints on the market, exclusive of the oxide paints, 
were applied to test plates and subjected to different conditions. 
Three plates were coated with each sample, one was exposed 
to the weather at the company’s works, a second was suspended 
half in air and half in water, and a third was submerged in 
the water of Chesapeake Bay. The tests extended over a 
period of ?. years, during the construction of the dock, and 
resulted in the choice of a mixture of red lead, white zinc 
and linseed oil in the following proportions: ioo pounds of 
red lead, 15 pounds of zinc ground in oil, and 5 gallons of 
linseed oil. It is only fair to state that in these tests a graphite 
paint manufactured in Detroit showed as good results as the 
red lead, but was not used because of the lack of available data 
bearing on its behavior in salt water. 

As the pontoons have more or less water in their bottoms 
at all times, except when self-docked, it was very necessary to 
provide adequate protection for their floors. Experiments with 
Bitumastic Enamel led to its application to the whole of the 
interior floors and to all vertical bulkheads, braces, etc., to a 
height of 12 inches. The process of applying this mixture 
consists in a careful cleaning and drying of the metal, one coat¬ 
ing of a solution the function of which is to provide a surface 



Fig. 1. —Self-Docking : Stern Pontoon Submerged 
Under Center Pontoon ; Bow Pontoon in Position 
Operation. 


and Drawn 
for Similar 



Fig. 2.— Self-Docking 


Side View, Showing Center Pontoon Docked. 


Face p. 204 









































































































. 



















• 




























FLOATING DRYDOCKS. 


205 


to which the enamel will adhere, and a final heavy coating of 
the enamel, from tV to |inch in thickness, applied hot. 

Great care was taken to rid the hull plating of mill scale. 
The specification provided that all loose scale should be re¬ 
moved by hammering, scraping and brushing with wire 
brushes, and to make its removal easier and surer, no paint was 
applied until a short time before launching. Nearly all the 
material, therefore, was exposed to the weather in the yard 
for periods ranging -from 12 to 24 months. The existence of 
mill scale on the completed structure has such an important 
bearing on the subject of corrosion that the additional expense 
entailed by pickling would be a good investment in the way of 
insurance, and it is recommended that specifications for future 
docks include this requirement. It was also noticed that, in the 
process of weathering, the mill scale, where covered with paint, 
adhered closely and could not be removed without the use of 
hammer and chisel. This scale, of course, will come off in 
time, and for this reason the requirement, that all contact sur¬ 
faces be given one coat of paint before assembling, should be 
limited, so as to apply to rolled shapes only. 

The contract ifor the dock was awarded on April 20th, 1903, 
and the first shipment of plates was received at Sparrow’s Point 
on July 17th. The first bottom plate was laid on the blocking 
on September 23d, 1903, and the dock was launched on Tune 
10th, 1905. The official ship docking and self-docking tests 
were held in the mouth of the Patuxent river, where the dock 
was towed immediately after the launching. A very com¬ 
plete description of the official tests by Civil Engineer A. C. 
Cunningham, U. S. Navy, Member of the Testing Board, was 
published in the Journal of the American Society of Naval 
Engineers,* and as the information contained therein may be 
desirable for purposes of discussion, it is deemed expedient to 
quote directly from that excellent paper. 

“The U. S. S. Colorado was docked on June 23, 1905, 
having a displacement of 13,300 tons at that time. The main 
and dockifig keel blocks were all set at the same height. In 


* Vol. XVII, No. 3 . 



206 


FLOATING DRYDOCKS. 


this preliminary test no effort was made to secure speed, and 
one-half hour was used in making flushing and fire connec¬ 
tions. The elapsed time from when the ship landed on the 
blocks until the keel came out of water was two hours and six¬ 
teen minutes. Pumping was continued until the dock had a 
uniform freeboard of two and one-half feet, only enough excess 
of water being retained in the side walls and end compart¬ 
ments to give the necessary trim. The Colorado was carried 
on the dock about twenty-four hours without changing the 
water ballast. When the dock had reached a freeboard of two 
and one-half feet with the Colorado, the deflection on the main 
keel line in the five hundred feet of length of the dock was 
about one-quarter of an inch; after about twenty-four hours 
the deflection in five hundred feet increased to about one and 
one-sixteenth inches. After undocking the Colorado the dock 
was found to have practically straightened without retaining 
any set. 

“After the undocking of the Colorado, deflection observa¬ 
tions were continued for three days, and variations in deflec¬ 
tions with the dock unloaded, due to temperature changes, of 
seven-eighths of an inch were noted. 

“The battleship Iowa was docked on June 27, 1905, for a 
record test, having a displacement of. 11,600 tons at the time, 
and was carried on the dock for forty-eight hours. The speci¬ 
fications required that a 16,000-ton ship should be raised in 
four hours from the time the ship took the blocks until the keel 
was out of water. For the equivalent of a 16,000-ton ship the 
dock was pumped to a freeboard of four and one-half feet. 
From the time the Iozm took the blocks until the keel was out 
of water was one hour and thirty-seven minutes; to the time 
the dock had a freeboard of four and one-half feet, two hours 
and forty-two minutes. During the docking of the Iozm one 
of the three pumping engines was out of commission for forty- 
two minutes with a slipped eccentric, so that the actual time 
of operation of the dock is about half that allowed by the speci¬ 
fication. 

“The Iozm was docked by uniform pumping, as in the case 






Fig. 2. —View of Dock, March i6th, 1904, Showing Bottom Plating 
in Place on Blocking in Building Basin, Main Pontoon Fram¬ 
ing, Etc. 


Face p. 206 









































































































FLOATING DRYDOCKS. 


207 


of the Colorado, and carried for iforty-eig'ht hours without 
change of water ballast in the dock. The specification required 
that when a ship had been docked by uniform pumping until 
the dock had a freeboard of two feet the deflection in the en¬ 
tire 500 feet of length of the dock should not exceed three 
inches. When the dock reached a freeboard of four and a 
half feet with the Iowa, the deflection was about two inches. 
During the first twenty-four hours, the dock remaining uni¬ 
formly pumped, the deflection increased to ifour inches in the 
500 feet, and during the second twenty-four hours showed a re¬ 
covery to three and three-eighths inches. 

“Immediately following the undocking of the Iowa the dock 
was pumped up to the same depth of water in the compart¬ 
ments as when the ship was docked, which gave a freeboard 
of nine feet and six inches, and it was found that the dock 
had a hog of one inch. During the night this hog disappeared, 
and early the next morning was a half inch sag. The greatest 
deflection in the bearing length of the Iowa while carried on 
the dock was about one and three-quarter inches. The deflec¬ 
tion observations indicate that there was no permanent set 
caused by the docking, and that temperature variations may 
cause considerable hog or sag. 

“After the undocking of the Colorado the main and dock¬ 
ing keel blocks were found to be uniformly indented about one- 
sixteenth of an inch with no crushing. No change was made 
in the blocks for the Iowa, and after undocking she was found 
to have rested even more easily than the Colorado.” 

During July the pontoons were successfully self-docked, and 
full particulars of this operation, by the writer, have also ap¬ 
peared in the Journal of the American Society of Naval En¬ 
gineers.* The total time consumed in the self-docking tests, 
exclusive of time spent on the blocks, was about 15 days, and 
it would seem probable that the time required for future self¬ 
dockings could be reduced to from 10 to n working days. 

The self-docking was in every way a success, but it may be 
of interest to call attention to one point which, while not affect- 




* Vol. XVII, No. 3 . 



208 


FLOATING DRYDOCKS. 


ing the safety of the structure, may yet be considered a defect 
of design. Preliminary to docking the center pontoon, it was 
necessary to disconnect the end pontoons and sink them to 
sufficient draught to allow them to be drawn under the center 
section. During the process of sinking the bow section, it was 
observed that after the pontoon deck was below the surface of 
the water it was very difficult to maintain longitudinal trim. 
First the forward end would sink more rapidly, and when this 
was checked by the valves the after end would forge ahead. 
This surging was not alarming, and would bring up within 3 
or 4 feet either way. The natural explanation of this action 
would seem to lie in the lack of symmetry of the horizontal 
section. When the deck is once covered with water, the flota- 


Connection end 



Fig. 20. 


tion of the pontoon having been destroyed, the excess flotation 
at X (Fig. 20), where the side walls come around the end, 
hold that end up while the other tends to go down. The oppo¬ 
site result was probably due to the momentum acquired by the 
bow when the forward valves were closed. It should be ob¬ 
served, however, that the stern pontoon did not surge, so that 
the explanation offered may not be the correct one. 

It is possible that the surging experienced in submerging the 












Fig. 1 . —View of Dock, May ist 1904; Bottom Peating and Bow 

Pontoon in Position. 



Fig. 2. —View of Dock, August ist, 1904, Showing 

Pontoons and Side Wades. 


Skin Peating of 


Face p. 208 




































FLOATING DRYDOCKS. 


209 


Algiei s dock may be explained by its pointed end pontoons and 
short side walls, and if this is true it would indicate that rec¬ 
tangular pontoons and full-length side walls are the best for 
stability during submergence. 

The Dewey has proven a complete success in every way. It 
has performed everything that was required of it, both as re¬ 
gards the docking of ships and the raising of its own pontoons; 
and it should be said here that the highly satisfactory results 
attained were largely due to the very evident desire on the 
part of the contractors to reach the highest mark in drydock 
construction, and the structure must stand as a monument to 
the executive ability and skill of their engineers. 

Any prediction as to the lines along which future develop¬ 
ment in floating-dock construction will take place can have only 
the value of a personal opinion, but it would seem, from the 
tendency of recent designs and the demand for a rigid struc¬ 
ture for naval purposes, that the solid-trough dock will again 
come into -favor. It is, without doubt, the ideal dock, and it 
would be generally adopted for naval use if it could be self- 
docked. It is possible that a designer may invent a plan or 
device for self-docking the solid dock, and, when this is an 
accomplished fact, it would seem that future advance must be 
confined to matters affecting the lifting capacity, structural 
strength and general convenience. 

The choice of power for operating the machinery is gov¬ 
erned by special circumstances, but the desirability of furnish- 
ing light and power to ships in dock may influence the more 
general use of electricity in the future. When located at repair 
yards the current could be supplied from power houses ashore^ 
and the dock could be provided with a generating plant for in¬ 
dependent operation, as in the case of the Pensacola ((formerly 
Havana) dock. 

To facilitate towing, the pontoons might be given a scow¬ 
shaped bow and stern, and, though involving considerable addi¬ 
tional expense, the corners might be slightly rounded without 
interfering to any great extent with the stability. Self-pro¬ 
pelled docks have been proposed, and such a dock is practical, 

H 


210 


FLOATING DRYDOCKS. 


but it is doubtful if there is yet a sufficient demand to warrant 
their serious consideration. 

It should be pointed out, in explanation of the incomplete¬ 
ness of this paper, that it is intended merely as a basis for a 
helpful discussion of a subject which must be of interest to 
all who are in any way connected with modern ships; and, if 
it should succeed in eliciting such discussion, its preparation will 
have been in a measure justified, despite its numerous and ob¬ 
vious shortcomings. 

Discussion. 

George B. Rennie, Esq.* (by letter).—The writer’s atten¬ 
tion was first called to the subject of floating docks when Mr. 
Gilbert, of the United States, undertook the construction of a 
wooden dock for the Imperial Austrian Government, at the 
Austrian Naval Arsenal, at Venice, which, when completed, 
was towed to Pola. Having taken great interest in the con¬ 
struction of drydocks, his grandfather, John Rennie, having 
done much in that line, and his uncle. Sir John Rennie, having 
written a book on docks and harbors, it seemed to the writer 
that the wooden floating dock, as constructed by Mr. Gilbert, 
had many advantages over the docks formerly used. 

On his return to England in 1852, he heard that General 
Quesada, Chief Engineer of the Spanish Navy, who had been 
to the United States and had seen the wooden floating docks 
in use at some of the naval arsenals there, had asked his firm 
whether such docks could be built of iron. As the writer had 
studied this question, he proposed an iron-plated floating dock 
.for the naval arsenal at Cartagena, Spain. There was an ex¬ 
cellent harbor at this place, but the shore was of soft rock with 
many crevices, etc., and, with much height and pressure of 
water, it was difficult to keep a drydock tight. For this reason 
a floating dock was well suited for this harbor. It was then 
proposed to excavate a shallow basin in which to place the 
dock in order to clean and repair it, etc. This plan was car¬ 
ried out, and the writer understands that the dock has been 


* Member, Institution of Civil Engineers. 




floating drydocks. 


21 I 


there ever since—more than 40 years—and when he last 

heard of it, it was in as good condition as when new. It was 

or is, 325 feet long, 105 feet broad, and takes a ship of 27 feet 

draught on 3-foot keel blocks; and lifts more than 4,500 tons. 

The Cartagena Dock was soon followed by one for Ferrol. 
Spain. 

In desiging these floating docks many new things had to be 
considered and proposed; the iron structure had to be made 
to float, and the ends of the dock left out. The wooden docks 
were built with pontoons at each end; this arrangement allowed 
of docking a ship longer than the dock itself. The dock being 
in one piece, was very strong. Tests were made at Cartagena 
by filling any compartment and pumping it out, independent of 
any other compartment, and the dock was made to heel over 
sideways, as well as at the ends, and righted again without 
danger or difficulty. A more detailed and constructive account 
of this dock will be found in the Minutes of Proceedings * of 
the Institution of Civil Engineers, and also in the Pranscictions\ 
of the Institute of Naval Architects. 

The iron dock for Ferrol was sent there, but was never com¬ 
pleted, a revolution having broken out in Spain. The pieces of 
plating, etc., were used for other purposes. It was 50 feet 
longer than the dock at Cartagena, and lifted nearly 1,000 
tons more. 

It may be mentioned that the bases of these docks were in 
single pieces riveted up, the means for cleaning and repairing 
being otherwise provided for. It was afterward arranged to 
have the bases divided into separate pontoons, so that the 
docks might be more easily launched, but where the base can 
be made in one piece it is better, as it is very difficult to con¬ 
nect the pontoons again after they have been in the water some 
years. 

It is a satisfaction to the writer, after having constructed 
these iron floating docks for 50 or 60 years, to learn that so 
much interest is being taken in the subject, and that the docks 


* Vol. XXXI, p. 295. 
tVol. X, p. 17. 



212 


FLOATING DRYDOCKS. 


have increased so much in number and size. This short ac¬ 
count of what has been done may not be of much interest, but 
the writer is glad to learn that the subject is being taken up 
before the American Society of Civil Engineers. 

J. R. Baterden, Esq.* (by letter).—The writer cannot ad¬ 
mit that the cost of a graving dock is greater than the cost of a 
floating dock of equal capacity and in a similar situation. A 
comparison of the costs, when completed, of No. 3 Dock, Nor¬ 
folk Yard, and the Charleston No. 1 Dock, leads one to the 
conclusion that the Dewey will have cost rather more than 
either of these. 

The writer’s experience in the construction of a large num¬ 
ber of graving docks is that in every case floating docks of 
equal capacity on the same sites would have been more costly. 
Moreover, in the confined situations to which docks and re¬ 
pairing yards have to be adapted in an industrial district where 
land is valuable, the floating dock, owing to the large amount 
of land taken up bv slopes, in cases where dredging is required, 
often renders its adoption an impossibility from a paying point 
of view. 

In one location where the writer had charge of the con¬ 
struction of graving docks, and where the water frontage was 
short and the work had to be carried on in a confined space, 
two graving docks were already in use, and another was being 
constructed, but, owing to high ground on three sides, and the 
soft nature of the foundation, it would have been impossible, 
without interfering with adjoining property, to have con¬ 
structed more than one floating dock of a capacity equal to 
one of the graving docks. 

In another place, however—a long narrow strip of land 
along the banks of the River Tyne—where two floating docks 
are in position, it would have been impossible to construct one 
graving dock of a capacity equal to the larger of the floating 
docks, without cutting up the yard in such a way as to detract 
seriously from its value. 

These examples show that, as a general rule, each location 


* Associate Member, Institution of Civil Engineers. 






FLOATING DRYDOCKS. 


213 


has to be considered on its merits, one suiting a graving dock, 
another a floating dock. There are few situations, however, in 
which a graving dock could be built in fairly good ground, 
where the writer would recommend a floating dock. 

As the author states, the expensive dredging which may be 
required, also moorings and shore connections, should be added 
to the cost of a floating dock for comparison with a graving 
dock, but in many cases this is not done. The dredging, which 
corresponds to the excavation required for a graving dock and 
much exceeds it in quantity, is in many cases a considerable 
item. 

Judging by the photographs, one is led to assume that the 
Dewey is moored in deep water, and possibly no dredging was 
required, but, if dredging were done, it would be interesting to 
know the cost. 

In the case of the two floating docks on the River Tyne, 
above referred to, the cost of dredging the site was about 14 
per cent, of the cost of the docks, and was a long and tedious, 
process, owing to the hard nature of the ground, in addition 
to which, the surrounding quays cost about 11 per cent. 

The ideal site for a floating dock is where deep water is 
available close to the shore. If the dock has to be placed some 
distance out, in order to ensure deep water without dredging, 
then connecting jetties may have to be provided; otherwise, 
most of the material required for repair will have to be trans¬ 
shipped to lighters, taken to the dock, and lifted on board, thus 
being handled twice; whereas, in the case of a graving dock, it 
would probably be brought to the side by rail. 

It is true that, except in rock, there is always an element of 
uncertainty about the foundations of a graving dock, which 
does not, to the same extent, enter into the calculations for a 
floating dock. 

The element of risk to vessels in the latest improved float¬ 
ing docks is not a serious one, and it is known that accidents 
have occurred to vessels in well-equipped graving docks. 

A floating dock can certainly be constructed in less time 
than a graving dock, but, if there is much dredging to be done. 


214 


FLOATING DRYDOCKS 


as in the instances above mentioned, and as in the case of the 
Bermuda dock, the time required might be much greater than 
the time occupied in building the dock, and even as long as in 
building a graving dock. 

The depth of water required for floating docks of the 
capacity of the Dewey with a 30-foot draught over 4-foot keel 
blocks, would be more than 50 feet. Thus, it would be beyond 
the working depth of dredges of any power and capacity, and 
the dredging would have to be done by special means, which is 
always costly. 

As the author says, if there be plenty of water under the 
bottom of a floating dock, one is not limited to the draught of 
ship taken on, as by the sill of a graving dock; but if dredging, 
especially of a difficult character, has to be done to obtain the 
necessary depth, it is unlikely that more than is absolutely 
necessary will be taken out, and the writer knows instances 
where the bottoms of floating docks rest upon the ground when 
sunk to receive a ship. 

Unless it be confined by quays, a floating dock does not, like 
a drydock, restrict the length of ship lifted, which is often a 
great advantage, but the advantage of adding sections to 
lengthen a floating dock when trade warrants, to which the 
author refers, is equally available by putting a temporary 
wooden end to a graving dock—not a costly item—and ex¬ 
tending the dock when required. 

The maintenance of floating docks is an item which, like 
their first cost, depends greatly upon circumstance, and there is 
not at present sufficient information to compare it accurately 
with the maintenance of graving docks, but it will be generally 
admitted that the latter is less. The dredging required from 
time to time, if the dock is in a location likely to be silted up, 
might be the larger proportion of the cost of maintenance 
(which may be anything up to ij4 per cent, per annum'on the 
first cost, or more), and has the disadvantage of being more 
uncertain than the cost of painting and docking. If, as in the 
case of the Dewey, where no re-dredging enters into the cost 
of maintenance, it amounts to 0.72 per cent, per annum on 



FLOATING DRYDOCKS. 


215 


the first cost, it will be seen that if, as in places the writer 
knows, floating docks are in locations where silting goes on 
at the rate of from 12 to 18 inches per annum, the cost of 
maintenance might easily be doubled, because, with such exces¬ 
sive silting, dredging may be required more frequently than 
cleaning or painting. 

Again, in the comparison of maintenance between a graving 
dock and a floating dock, it must be noted that ordinary re¬ 
pairs could be executed and re-dredging done outside while 
vessels were in the graving dock undergoing repairs, whereas, 
in the case of the floating dock, for any dredging required, the 
dock has to be removed tfrom the site, and in this case, as in 
docking and painting, the whole of the work is stopped. 

As regards pumping, as far as the British Isles are con¬ 
cerned, with the high range of tides available, unless the grav¬ 
ing dock be entered from a basin, or the ship be of the maxi¬ 
mum capacity of the dock, the draught of ship regulates the 
quantity of water to be pumped, as ships can be admitted at 
different stages of the tide, some requiring more water than 
others; whereas, on the southern and eastern seaboard of the 
United States, for 1,500 miles or more, there is no appreciable 
tide, and on the remainder of the coast, east and west, the 
highest tides are only about equal to the lowest of those on the 
British coasts, and pumping would be much the same for all 
ships. Hence, in seas where the tidal rise is very small, the 
advantage of pumping is largely in favor of the floating dock. 

The writer knows of no place on the British coasts where 
deep water, such as required by the Dewey, could be available 
except in a situation so exposed as to render it impracticable. 

The moving of a large floating dock from site to site has so 
many objections that, from a commercial point of view, it 
could not be entertained. The loss of the floating dock while 
being towed from the Tyne to Durban, the grave fears which 
were entertained as to the safe arrival of the Dewey in the 
Philippines, the fact that these craft, with side area approach¬ 
ing the sail of a full-rigged ship, with the disadvantage of not 
being able to reef it, exposed to the action of wind and sea 


216 


FLOATING DRYDOCKS. 


when being towed along a coast line or taken up rivers, the 
great cost of towing and insurance, however necessary it 
might become from a strategic point of view in time of war. 
must necessarily be very costly, and would entail the pres¬ 
ence of a small fleet for protection. 

It will be seen, then, that graving docks and floating docks 
each have their advantages ; there is scope for both, and, in 
coming to a decision as to the selection of either, many things 
have to be taken into consideration. 

Cecil H. Peabody, Esq.* (by letter).—This paper has the 
double interest that comes from a full description of the Dewey 
—the most important floating dock—and from a detailed state¬ 
ment of the computations for strength and stability. With such 
a wealth of computation, compressed as it must be for pre¬ 
sentation in a paper of fifty pages, one can grasp at the first 
reading only the methods and general results, with perhaps a 
casual question or two. For example, on page 184, the ques¬ 
tion arises: What was the distance from the keel to the bilge 
blocks? To be sure, a little puzzling over the figures leads to 
the conclusion that the distance must have been 22 feet. Again, 
the specifications require the dock to be able to dock all classes 
of ships, either centrally or with the keel 1 foot off center, but 
no mention appears to be made of this'in the calculation of the 
stability, nor is there any statement of the probable inclina¬ 
tion of the dock under the assumed wind pressure of 30 pounds 
per square foot. As for eccentric loading', it is easy to see 
from Fig. 19 that a 16,000-ton ship, 1 foot off center, will 
give an inclination of only ij4° in the worst condition. 

One of the most interesting features of the paper is the dis¬ 
cussion of the proper thickness of the outer shell plating. The 
author concludes that “all attempts to derive a rational for¬ 
mula for them in flat plates have resulted in complicated expres¬ 
sions too cumbersome for practical use,” and, if he had it not 
in mind, would doubtless include in this category a paper by 
Ivan G. Boobnoff, I. R. N., “On the Stresses in a Ship’s Bot- 

* Professor of Naval Architecture and Marine Engineering, Massachusetts Institute of 
Technology. 



FLOATING DRYDOCKS. 


2I 7 


tom Plating Due to Water Pressure.” * Truly, the computa¬ 
tions required by his method, even with aid of the special 
tables which he provides to save labor, would ordinarily be 
considered to be complicated, though it appears to the writer 
that too high a price can hardly be paid for computations which 
lead to reliable results. 

It may be interesting to know that observations were made 
on the deflection of the rectangular panels of the inner plating 
of the double bottom qf a certain warship, when tested under 
water pressure, by an assistant naval constructor who, at the 
time, was studying at the Massachusetts Institute of Tech¬ 
nology. The results showed a fair conformity with the theo¬ 
retical calculations made by Boobnoff’s method. This work, 
which was under the direct supervision of Captain Hovgaard, 
Professor of Naval Design, it is hoped will be carried further 
and will be used as the basis of a logical determination of the 
proper thickness of shell plating, or the proper spacing of 
frames. Meanwhile the best practical guide is unquestionably 
the common practice in ship building, as given in tables of 
scantlings furnished by marine insurance companies and asso¬ 
ciations, or, as may be inferred, from practice in warship de¬ 
sign. 

The results qf the experiments, referred to by the author on 
page 188, will be awaited with much interest, though it is to 
be regretted that the plates were supported only at their edges 
and were not continuous over the supports. 

C. Colson, Esq. 1 * (by letter).—A cardinal point presented 
for consideration by the author is whether there are advantages 
attaching to the floating dock which are of such a character 
and economic value as to outweigh those offered by the sunk 
or drydock, both for commercial and naval purposes, but with 
special reference to the latter. 

No question arises as to the possibility of designing a float¬ 
ing dock of dimensions, strength and stability capable of lift¬ 
ing the largest and heaviest ship constructed or contemplated. 


* Transactions, Inst, of Naval Architects, Vol. XLIV, p. 15. 
t Member, Institution of Civil Engineers. 




218 


FLOATING DRYDOCKS. 


Recent examples of floating-dock construction conclusively 
prove this point. 

There are places where the construction of a dry or sunk 
masonry dock would be, practically, an impossibility, or where 
it could be accomplished only at an enormous outlay; in such 
a case the only alternative would, probably, be the floating 
dock. 

Among the many points to be taken into consideration with 
special reference to the floating dock are: Water area avail¬ 
able in a convenient and sheltered position for berthing such a 
dock without obstructing navigation or interfering with wharf¬ 
age ; depth of water on any available area at low tide; draught 
of water required over the sill or keel blocks; character of the 
ground to be removed in order to obtain the depth of berth 
required: the class of vessel to be dealt with, and the use for 
which a dock is required; and, whether the depth of water over 
the keel blocks or sill should be for light or full-load draught? 

Even for commercial purposes, it appears desirable that the 
power of docking at full-load draught at low water of spring 
tides should be available, although such a facility may not 
be often in demand. With regard to naval ships, not only is 
it essential that the power of docking at full-load draught at 
low water be provided, but there must be a margin of depth 
to admit of a seriously damaged ship being docked at low 
water. These requirements will increase the depth, and, conse¬ 
quently the first cost and subsequent maintenance of the berth, 
and augment the ancillary works. 

Where docking is required for cleaning and coating, or for 
the execution of minor repairs, the floating dock is eminently 
fitted, but, in cases where extensive repairs are required, in¬ 
volving the manipulation of heavy weights and the employ¬ 
ment of a large number of men, the conditions become more 
complicated, and, in the writer’s opinion, indicate the adoption 
of a drydock, from the point of view that heavy weights can 
be handled with greater facility, resulting in the saving of time 
and labor; further, a ship in a drydock is under more com¬ 
plete observation from the wharf, and in case of fire is much 
more accessible. 


FLOATING DRYDOCKS. 


219 


\\ ith legald to the comparative cost of a steel floating dock 
and a masonry drydock of equal docking capacity, there are so 
few data available as to the cost of the different items making 
up the complete installation, that any general statement must 
be fallacious* a reliable comparative estimate is only possible 
after careful consideration of the conditions obtaining in each 
case, and the preparation of alternative designs in detail. The 
total cost of installation should include the acquisition of the 
site of the berth and any other areas required in connection 
w ith the dock; the cost of the dock, complete; the conveyance 
from the place of construction to the permanent site; the prepa¬ 
ration of the berth, moorings, shore facilities, including wharf 
walls or settees, shops, stores, etc.; and, means of communica¬ 
tion between the dock and the shore. I11 this connection any 
information that the author can give as to the installation o ( f 
the floating dock Dewey will be most valuable. 

The time required to install a floating dock, complete in 
every particular, is not always determinable by the time re¬ 
quired to construct the dock itself; it must depend greatly on 
the character of, and time required to complete, the ancillary 
works. 

It is suggested that no land space is required in connection 
with a floating dock. This view will hardly hold good in all 
cases, or in the majority of cases, where a floating dock is re¬ 
quired for cleaning and coating a ship and for minor repairs. 
It is conceivable that it might be moored in a position in the 
open, but even then it might be necessary to acquire the area 
of the harbor bottom for the berth. Where a dock is required 
in connection with an existing shore establishment, with water- 
frontage rights and wharfage, of course, a very, considerable 
outlay will be avoided; but, failing any existing water and land 
facilities, a very substantial expenditure in this connection will 
be necessarv. 

m/ 

Idle greater the width required on the floor, the greater 
will be the depth of the bottom member of the dock, and, con¬ 
sequently, the greater will be the total depth of the berth; 
while the area to be dealt with will be increased by the slopes 


220 


FLOATING DRYDOCKS. 


necessary to ensure the stability of the sides, 59 to 60 -feet 
would not be an excessive depth below low water for a dock 
with a draught of 35 feet over the keel blocks. This would 
probably mean the maintenance of a hole 24 or 25 feet deep, 
below the approach channel; or, the bottom of the harbor, if 
the berth is to be located in deep water. The preparation of 
such a berth might be a long and costly operation, unless under 
very favorable circumstances. A site might be found with an 
ample depth of water at low tide, but such a case would be 
exceedingly rare, and then only at a very inconvenient distance 
from the shore. 

With regard to the author's remarks as to the comparative 
power of floating and drydocks, he must refer to drydocks 
constructed to take in ships of maximum draught at high tide 
only, or, at any rate, not at low water. In drydocks of modern 
construction the sills and floors, as a rule, are designed so that 
battleships of the greatest draught can be docked at low spring 
tide. Therefore, the advantage may be taken as being with the 
drydock, inasmuch as the rising tide will increase the avail¬ 
able depth of water over the sill or blocks. The exceptions to 
this are docks opening into a practically tideless harbor, or 
into closed basins where, however, the water, as a rule, can 
be raised 1 or 2 feet by pumping. 

A floating dock, when raised with a ship upon it, would be 
a very prominent target, and would be far more susceptible of 
damage from shell fire than a sunk dock. A suggestion is 
made that in an emergency the floating dock would have the 
advantage, inasmuch as it could be towed to a place, or places 
in succession, of greater safety. This, of course, would be 
possible, but'does not the suggestion presuppose the provision 
and maintenance of emergency sites and moorings—adjuncts 
which cannot be prepared at very short notice even from a 
temporary point of view? 

In the case of a badly-damaged war vessel with a heavy 
list and all her weights on board, it is the writer’s opinion that 
she would be placed with greater confidence in a drydock than 
on a floating dock, because in the former the facilities for the 


FLOATING DR V'DOCKS. 


221 


removal or adjustment of weights, with a view to getting the 
vessel upright, would be greater than in the latter. It has been 
suggested, however, that the floating dock could be trimmed 
(i. e., listed) so as to accommodate it to a listed ship, and the 
vertical position restored with the rising of the dock. This 
view is probably correct to a limited extent with a sectional 
dock, when dealing with vessels floating light—especially com¬ 
mercial vessels—and, to a greater extent, with the solid type 
of floating dock, but it is a doubtful point as to how far a 
heavy, deep-draught battleship with a bad list could be thus 
dealt with on a sectional floating dock, bearing in mind the 
character of the ship’s bottom, the distribution of weights, and 
consequently the risks involved by insufficient or irregular sup¬ 
port. In this connection it would be interesting if recorded 
details of any such operations could be quoted, and the opinion 
of the author and other experts would be of great value. 

Although no doubt exists as to the possibility of lifting the 
largest and heaviest war vessel, under favorable conditions, 
there are risks and difficulties attending the docking operations 
on, and subsequent use of, a floating dock, which do not obtain 
in the docking operations, and subsequent use of, a drydock. 
While the disabilities, by design, care in manipulation, and 
forethought, may be reduced to a minimum, they cannot be 
entirely eliminated. The balance of argument, therefore, re¬ 
mains in favor of the drydock, especially for naval purposes. 
At the same time the writer fully concurs with the author’s 
remark, “that each type has its own particular field of useful¬ 
ness which the other cannot with advantage fill;” therefore, no 
thoughtful engineer will fail to recognize the value of the 
floating dock, or hesitate to recommend its adoption where the 
conditions undoubtedly indicate its adaptability in preference to 
a drydock, although his bias may be in favor of the latter. 

A. C. Cunningham, M. Am. Soc. C. E. (by letter).—Mr. 
Cox has treated the subject of floating dry docks so thoroughly 
and so ably, that there remains but little to say in the way of 
discussion which will not be a repetition of his ideas in a dif¬ 
ferent form, or an enlargement upon the same. 




222 


FLOATING DRYDOCKS. 


The short and certain time in which a floating drydock can 
be constructed may be an important factor, both from a 
commercial and a military point of view. From the actual 
records of the time of construction of various docks, and the 
observation of what might be the possible rate of progress of 
construction, it is safe to say, that, in emergency, a floating 
dock of the first magnitude could be built in a year. If such 
a dock was also of the sectional type, each part complete in 
itself, the time of construction might be still further reduced. 

The possibility of manufacture in one or more places and 
of final assemblage and erection at the destination are also of 
great importance from the commercial and military points 
of view, especially from that of the latter. Since the trip of 
the Deive\ it is an established fact that a floating drydock can 
be towed anywhere with certainty and safety. Such towing, 
however, is a slow and tedious operation, and in time of war 
would be attended with several apparent risks, all of which 
can be eliminated by the erection of the dock at its destination. 

The British and Japanese Governments have just demon¬ 
strated that 20,000-ton battleships can be built in a few 
months. This is a demonstration that radical departures and 
advances in ship building may occur at any time in the future. 
When such departures and advances can not be cared for with 
existing masonry docks, they are still rendered possible by* 
floating docks. No matter what length, beam and draught 
may be given a ship, a floating dock that will accommodate it 
can be built and put in operation in less time than the ship 
can be constructed. 

Increased and careful attention is being given to the dock¬ 
ing of ships which may have abnormal draught from acci¬ 
dent. To provide for this contingency with a masonry dock 
means not only greatly increased difficulties and cost of con¬ 
struction. but a continuously increased cost of maintenance, 
and more especially operation. 

The floating dock is an ideal structure for dealing with 
ships at abnormal draught. Its increased cost for this condi¬ 
tion is a trifle; there are no increased difficulties of construe- 


FLOATING DRYDOCKS. 


223 


tion; the increased cost of maintenance is hardly preceptible; 
and, the cost of operation for ordinary conditions is not in¬ 
creased at all. 

While the desirability of a floating- dock for dealing with 
ships at abnormal draught is becoming recognized, general 
attention has not yet been called to its possibilities as an auxili- 





Fig. 21 









































































































































































































































































































224 


FLOATING DRYDOCKS 


ary to masonry docks for this condition. The masonry docks 
of the future must accommodate the length, beam, and nor¬ 
mal draught of the ships which they are to dock, but if they 
are to accommodate also the possible abnormal draught which 
may occur, it means a large and constant outlay of money for 
which there will seldom be a return. From a military point 
of view, abnormal draughts will occur in groups at unknown 
intervals, and may be with our own or captured ships. 

With a suitable distribution of floating drydocks, the pro¬ 
vision ifor abnormal draught in masonry docks may be dis¬ 
pensed with, and the increased first cost of constructing and 
the continual excess cost of pumping avoided. With such a 
combination the ship would be lifted first by the floating dock, 
such temporary repairs would be made as would restore nor¬ 
mal draught, and the ship would then be placed in the masonry 
dock for complete and final repairs. At first thought it would 
seem that one deep-draught masonry dock in a suitable group 
would fully meet the requirements, but the mobility of the 
floating dock again introduces special advantages. Abnormal 
draught, in any event, means a dangerous condition, and may 
mean that a ship can not pass through a harbor or regular 
channels in order to reach a masonry dock. In such an event 
the floating dock can go to a place where the ship can be lifted, 
and, as the draught of the combination will be small, the com¬ 
bination of dock and ship can be towed to a place of shelter 
and safety. One important requisite in docking a ship in a 
floating dock is that there shall be no independent and un¬ 
controlled vertical motion in either. In extreme cases, how¬ 
ever, as the saving of a battleship, even some vertical motion 
might be safely risked by suitable padding the deck of the 
dock with timber. 

Floating docks located at the entrance of New York Har¬ 
bor, the mouth of the Delaware river, the entrance of Chesa¬ 
peake Bav, and in the harbors of San Francisco and Pueet 
Sound, might, in saving one or at the most two battleships, 
more than return the cost of all the docks together. 

A floating dock in connection with a floating repair plant 


FLOATING DRYDOCKS. 


225 


constitutes a lepaii station that can be taken anywhere. The 
lepaii plant can also be in the form of barges which can be 
placed on the deck of the dock when a move is desirable. 

As to convenience and accessibility in use: If a floating 
dock is moved into a slip after lifting a ship, the bottom is 
moie accessible to workmen than in the case of a masonry 
dock, and, with a suitable gantry crane, everything movable 
on the ship can be handled more conveniently and safelv than 
with the jib cranes used around a masonry dock. With a 
suitable depth of water in the slip this same gantry crane would 
be far more desirable for handling the heavy weights on ships 
that aie not docked than the shears and jib cranes now gen¬ 
erally used. 

In the matter of possible accident the floating dock, theo¬ 
retically, is more exposed than the masonry dock. In this 
matter, however, every dock, whether masonry or floating*, 
must be judged by its special conditions. A masonry dock, 
however safe and perfect in other respects, may always have 
its caisson rammed, and, with a ship in dock, such an acci¬ 
dent would be very serious. A floating dock in an entirely 
exposed position may be rammed from all sides, but, if empty, 
such an accident would not result in the loss of the dock, on 
account of the very numerous watertight compartments, and, 
for the same reason, if a ship were in the dock, the damage 
to it is not likely to be as great as in the case of the rammed 
caisson of a masonry dock. If a floating dock is placed in a 
slip with a level bottom not much below the bottom of the 
dock, ramming from any very heavy ship is impossible, and 
any serious sinking from failure of valves is guarded against. 
Floating docks are entirely free from failures of foundations 
due to quicksands, springs, and the hydrostatic pressure to 
which all masonry docks are more or less exposed. The 
caissons of masonry docks may fail from other causes than 
ramming, and, in the case of an isolated dock having no 
spare caisson, such a failure might put the dock out of com¬ 
mission for several months. 

For certainty of preservation and repair, it has been neces- 

15 


226 


FLOATING DRYDOCKS. 


sary so far to make steel, floating drydocks self-docking. This 
feature not only complicates the construction and increases 
the cost, but is a source of more or less weakness, according 
to the number, location, and complication of the joints which 
connect the various parts of the dock. To eliminate the self¬ 
docking feature, the writer proposes an independent caisson 
for the repair and preservation of the bottoms Qf solid docks, 
which, if it can be made effective, will simplify the floating- 
dock problem. 

The proposed caisson is illustrated in Fig. 21, which is dia- 
gramatic, and for purposes of explanation only. 

The action of the caisson is as follows: Caisson floating* 
light with main and supplemental chambers empty; main 
chamber opened, and water freely admitted; complete submer¬ 
gence is prevented by the supplemental chamber. Water is 
next admitted to the supplemental chamber until buoyancy is 
just destroyed : the caisson then sinks until arrested by lines or 
supplemental floats. In this condition the caisson is moved 
under the bottom of the dock. Expelling the water from the 
supplemental chamber causes the caisson to rise and seal 
against the bottom of the dock; the water is next expelled 
from the main chamber, causing a still firmer seal against the 
bottom and providing a space in which work may be per¬ 
formed. The edges of the dock may be worked on by canting 
out of the water, or the caisson may be sealed against the bot¬ 
tom with the supplemental chamber and with one end pro¬ 
jecting; after the edge of the dock is canted out of the water, 
the main chamber may be emptied; a working platform is thus 
provided. It is evident that entrance shafts and supplemental 
floats are not essential, as the caisson could be controlled by 
lines, and access had through a manhole in the bottom of 
the dock after the caisson was sealed. 

If the self-docking feature of floating drydocks can be elimi¬ 
nated, a valuable gain will be secured. Not only do self¬ 
docking features increase the cost and complication of a dock 
and cause weakness on account of the necessary joints, but 


FLOATING DRYDOCKS. 


227 


the self-docking of itself causes a loss of valuable time which, 
at least, may amount to ,from one to three months. 

If a successful caisson method can be devised for working 7 
on the bottom of a dock, no time whatever need be lost unless 
it is in working' on the edges of the dock, and, furthermore, it 
will be possible to carry on work while a ship is in the dock. 

Lyon el Clark, Esq . * (by letter).— I he writer has read 
this paper with much interest, especially that portion which 
deals with the calculations of the strength of the parts of a 
dock and of a dock as a whole. Many years ago, when the 
writer’s firm t first took up dock designing, calculations were 
conspicuous by their absence; but his firm has gradually built 
up a collection of rules which are found very useful in the 
rapid determination of the parts of any given dock. It is also 
interesting to note that the justifications arrived at are practi¬ 
cally the same as those in Mr. Cox’s paper, so that the condi¬ 
tions under which the Algiers Dock was designed are practi¬ 
cally the same as those which governed the construction of the 
Dewey. 

Calculations for a dock, however, are somewhat like those 
o f f a ship: they are of great value if used as a guide for what 
is required rather than as a rule; for, as in the case of ships, 
there are many portions of a dock in which experience alone 
can determine what extra strengthening is required, or what 
portion may be lightened. A notable case in point is the deter¬ 
mination of the required thickness of the skin plating to with¬ 
stand a certain head of water. In the Cavite Dock, the per¬ 
missible working stress was extraordinarily low. Mr. Cox 
appears to recognize this, and gives a supplementary curve 
(f) which he bases on experimental deflection. It is of inter¬ 
est to note that this curve follows closely that which would 
be given were the plating considered as a continuous beam 
uniformly loaded with a permissible stress on the material of 
7 tons per square inch. The writer’s experience, however, is 
that much higher stresses than this can be safely supported. 


* Member, Institution of Naval Architects; Member, Institution ot Civil Engineers, 
t Messrs. Clark and Standfield, of Westminster, England, and Washington, D. C. 




228 


FLOATING DRYDOCKS. 


Fortunately, the thickness of the skin plating of a dock is 
very frequently subservient to other conditions than mere 
stress considerations, but, where this is not so, in general prac¬ 
tice, the writer’s firm assumes the plating as a beam working 
at a stress of about 8 tons, and has, indeed, gone to higher 
figures than this, the highest, as a matter of if act, amounting 
to about 12 tons per square inch. This was in a small dock 
built some 20 years ago, which, however, is still in use, and 
has certainly shown no signs of weakness. 

In the case of the Rotterdam Town Dock, also, which has a 
lifting power of 15,000 tons, the stress on the bottom plating, 
according to the published plans, would work out, if consid¬ 
ered as a beam, at not less than 14^2 tons per square inch, and 
it is believed that this dock, which has now been in service 
for the last two or three years, was built entirely according 
to the specification. It is evident, therefore, that skin plating 
does not behave solely as a beam, but, to a very great extent, 
as a suspended or stretched cord; and, although it is difficult 
to justify by calculation to what extent this action takes place, 
it is abundantly demonstrated by practice that, when consid¬ 
ered as a simple girder or beam, skin plating may be stressed 
safely to considerably more than what would be allowed in 
other portions of the dock. 

The other calculations, as already mentioned, follow pretty 
closely the practice of the writer’s firm, and as his firm pre¬ 
pared a complete scheme for the Cavite Dock (which scheme, 
however, owing to the late arrival of necessary information, 
could not be completed in time for submission to the authori¬ 
ties), he is enabled to compare somewhat closely the scantlings 
proposed and those actually used in the Dewey. The differ¬ 
ence is very slight, and although the type of dock worked out 
about 500 tons lighter than the Dewey, this was doubtless due 
to the fact that the design was of the “Bolted Sectional,” or 
“Pola” type, as Mr. Cox calls it. This type, of course, re¬ 
quires fewer transverse bulkheads than the Dezvey type, and 
the extra side walls on the end pontoons are also unnecessary. 

While mentioning this Pola type of dock, the writer desires 


FLOATING DRYDOCKS. 


229 


to criticize some of the author’s statements as to the advan¬ 
tages or otherwise of this type, and must still hold to his 
claim that the Bolted Sectional is the strongest type, even 
when compared with the Dewey. As regards the walls of this 
dock, and that portion of the pontoon above the light water 
line, these bolted sectional docks can be, and sometimes are, 
completely riveted up, so that the walls, the pontoon deck, and 
some of the side plating of the pontoons, are practically as 
continuous a dock as the Dewey, and only the extreme bottom 
edge of the pontoon has to be joined by bolts. The writer 
cannot help thinking that anyone must readily admit that a 
continuous line of close-pitched bolts running all around the) 
bottom edge of the pontoon of a dock must be a considerably 
stronger form of joint than the vertical lugs shown in the 
Dewey, which—if he may be permitted to say so—somewhat 
recall that old engineering paradox of how the flange of a 
girder may be weakened by adding fresh material in the form 
of an extra web on top of it. However, be that as it may, 
there was no difficulty in designing and justifying a bolted 
sectional dock, under the Cavite conditions, that gave the re¬ 
quired strength everywhere, and this, indeed, without having 
to deepen the side girders. 

Mr. Cox also seems to be under a slight misapprehension as 
to the self-docking of this type of dock. The bolted under¬ 
water joint is nothing new, but has been used by the writer’s 
firm for years past; indeed, it is now thirty years since he him¬ 
self made and worked his first joint of this type, which is still 
in satisfactory condition, and since then many other docks 
have been joined by the same system, and, thus far, none of 
the difficulties foreseen by Mr. Cox have presented themselves. 

As regards the self-docking itself, although in the sketches 
the lands upon which the lifted portion rest appear to be very 
small, in practice they are of considerable length, and, gener¬ 
ally speaking, a still further length of the pointed ends of the 
pontoon can also be utilized to give bearing surface. In the 
case of a large bolted sectional dock which Messrs. Clark & 
Standfield are now designing for Germany (which has a lift- 



230 


FLOATING DRYDOCKS. 


ing power of 36,000 tons), the docking lands are more than 
12 feet long, and in addition to this, the points project some 
50 feet below the remainder of the dock, and can be utilized 
as supports if required. 

That still water is necessary for self-docking this type of 
dock is self-evident ; and, indeed, still water is necessary for 
any other self-docking system with which the writer is 
acquainted. If anything, the bolted sectional dock should be in 
a more favorable position, because it is evident that the larger 
and heavier the separate sections to be handled, the less move¬ 
ment they will have in a given seaway. 

With regard to the author’s general conclusions as to the 
line on which future developments in floating-dock construc¬ 
tion will take place, the writer is certainly in agreement with 
them, but with some modifications. The “Box” or “Solid 
Trough” dock is doubtless an ideal design, but there are great 
difficulties in its construction if it is to be of any size. There 
are but few sites where a dock could be built in a basin and 
floated out as a whole, and the difficulties of launching a dock 
as large as the Deivey, in one piece, from ordinary launching 
ways, would be very serious indeed. It becomes necessary, 
therefore, if the dock is to be built by ordinary ship builders, 
to construct it in sections, and, if it ha's to be built in sections, 
it is certainly advantageous to arrange them so that they can 
self-dock the remainder of the structure, the more so, as the 
writer most strongly holds, that the joints between such sec¬ 
tions can be made as strong as the remainder of the dock. 
This could be done equally well whether the Dewey or the Pola 
type were adopted, and the writer would here like to express 
his appreciation of the ingenuity of the iformer design, which, 
if the dock has to be square-ended—as was specified in the case 
of the Cavite Dock—and especially if the end pontoons were 
bolted to the main structure after the manner of the Pola 
type—which would be perfectly feasible—he would consider 
as complete a solution of the problem as one could possible 
devise. 

This question, however, as to whether a dock should be 


FLOATING DRYDOCKS. 


23I 


square-ended, raises many considerations. The specification 
for the Dewey calls for a long dock of uniform buoyancy, and 
then bristles with all sorts of conditions as to how it is to be 
built in order to carry a short and heavy ship resting only over 
a portion of its length—in other words, to act as a short dock 
—these conditions being carried to such an extent that the ship 
is assumed to be a flexible mass, which, of course, is an impos¬ 
sibility. It is a mistake to carry the (full lifting power of the 
dock over its whole length, and the writer is strongly of the 
opinion that the ends of a dock should be in the form of points 
having much less buoyancy than the remainder of the dock, 
and, indeed, at the extreme ends only working platforms are 
necessary. 

It is interesting to note here, that, in spite of the low theo¬ 
retical working stress allowed in the Dewey, when the Iowa 
Avas lifted, the deflection of that vessel was about inches. 
The Bermuda Dock, which has but little more than half the 
weight of the Dewey, and was built under no special condi¬ 
tions as to longitudinal strength, when lifting the battleship 
Dominion , which had a displacement of 16,380 tons, at the 
time of docking, produced a breakage on this vessel of only 
inch, although, since then, under certain conditions of tem¬ 
perature, it has deflected as much as 1 % inches. This is solely 
due to the fact that the lifting power of this dock was mainly 
concentrated under the bearing length of the ship, the pointed 
ends giving but feeble buoyancy in comparison with the re¬ 
mainder of the structure. 

The writer is very strongly of the opinion that, where the 
depth of water will permit, instead of putting metal into the 
Avails of the dock in order to make them stiff enough to bear 
a concentrated load over the middle of the dock, this metal 
should be put into the pontoons so as to increase the lifting 
power, and make this practically equal to the Aveight of the 
ship bearing on the dock and concentrated under the same. 
This point has been emphasized most strongly in his mind 
when designing the large bolted sectional dock previously 
alluded to. This dock, which has a length of 721 feet 6 inches 


s 



232 


FLOATING DRYDOCKS. 


over all, has a mean lifting power of about 55 tons per foot 
run over the square portion. This means that it can oppose 
a lifting power per foot run considerably greater than the 
weight per foot run of any ironclad built or building, and. 
indeed, such a weight is only just attained by the huge quad¬ 
ruple-turbine Cunard steamers now nearing completion, and 
for the lifting of which, or of vessels of similar size, this dock 
was designed. That this increase in lifting power is not 
attained at great expense may be shown by the fact that this 
dock has only 10,000 tons of steel in its hull, that is to say, 
but very little more than the Dewey , although it is of twice its 
lifting power. 

In conclusion, therefore, the writer’s opinion is that the 
dock of the future should be self-docking, and approaching as 
nearly as possible to the “Trough’' or “Box" dock in strength, 
but with a lifting power per foot run in its pontoons superior 
to the unit weight of the biggest ships with which it has to 
deal. The end sections, coming under the overhanging bow 
and stern of the ship, should be of much lighter construction 
and of small buoyancy, if any. With a dock of this sort, all 
deflection of the ship would be absolutely eliminated; indeed, 
if necessary, a contrary deflection, that is, a “hogging" effect, 
might be placed on the ship, and, in short, the docking berth 
on a dock of this type would approach as closely as possible 
to the support afforded by the bottom of an ordinary excavated 
masonry dock, which, for heavy ironclad and armored cruis¬ 
ers, it must be admitted, is as nearly as possible the ideal solu¬ 
tion of the problem of supporting suitably a vessel, which, as 
Sir William White says, has a bottom which is comparatively 
an egg-shell. 

Edward Box, Esq.* (by letter).—The writer has been 
much interested in this most excellent paper. 

In Great Britain, floating docks, in most cases, have been 
adopted only where the site has rendered it impracticable to 
build a graving dock. 

The facilities offered by the surroundings of graving docks. 


* Associate Member, Institution of Civil Engineers. 



FLOATING DRYDOCKS. 


233 


recessed as they are into the land, apart from the actual method 
o ; f docking, have doubtless favored the adoption of this type; 
but the fact remains that a great many ship owners give the 
prefei ence to floating docks, when the two methods are equally 
obtainable. A good example of this is seen at the Smith’s 
Dock Company’s works, at the mouth of the Tyne. 

The company has eight drydocks and a ship-building yard. 
Two of the docks are floating docks of the off-shore type. A 
fair idea of the business done by this company can be obtained 
from the fact that, for purposes of painting and repairing, 
nearly 800 vessels pass throiigh its hands every year. 

Regarding the floating dock from a dock owner’s point of 
view, the periodical self-docking is tiresome, and, in locations 
where silting is rapid, the steady but persistent loss in depth 
Off water is most troublesome. Yet the many advantages pos¬ 
sessed by the one-sided floating dock, not the least being its 
rapidity of action, are likely to keep it in favor as a docking 
machine for commercial purposes. 

The author, not unnaturally, has referred to Mr. Lyonel 
Clark’s paper before the Institution of Civil Engineers, and as 
the writer, in his contribution to the discussion on that paper, 
criticized the several known types described by Mr. Clark, he 
does not think it necessary to repeat his remarks here, as un¬ 
doubtedly those interested in the subject will have read Mr. 
Clark’s paper. It was in Mr. Cunningham’s discussion of that 
paper that the type of dock with which the author deals first 
came to the writer's notice. 

There can be little doubt that the nearer we keep to the 
simple box form of floating dock, the stronger it is possible 
to design. The type of dock which the author describes would 
appear to solve more nearly the problem of a two-sided or self- 
contained floating dpck than most designs which the writer 
has seen; but, until auxiliary constructional works are entirely 
dispensed with the problem cannot be considered to have 
been entirely solved. 

The difference in the quantities of water pumped in the 

* 

two systems of drydocks, as given by the author, is interest- 


234 


FLOATING DRYDOCKS. 


ing. In a similar calculation made some time ago, the writer 
took the total number of vessels actually docked in a graving 
dock and in a floating dock of nearly the same dimensions for 
a period of one year, and found the quantities of water to be 
as follows: Graving dock, 8,200 tons; off-shore dock, 3,5°° 
tons. As no account is taken of emptying for blocking pur¬ 
poses, the difference at times is much greater. 

This difference may not be of very great moment in the case 
of Government docks, at least in places where coal is reason¬ 
able in price, but it certainly is of great importance in that of 
commercial docks, more especially large docks where small 
vessels often have to be accommodated. 

Based upon experience, the writer is strongly of the opinion 
that long pointed ends are a mistake, and, for purposes of con¬ 
trol in working, the sides should be carried not necessarily the 
full length of the dock, but nearly so. 

It is interesting to note that the Dewey was constructed in 
a basin. The writer would not like to be too confident as to 
who first suggested the shallow basin for floating-dock con¬ 
struction, but the method was strongly advocated by the late 
John Standfield, and adopted by his firm at Gray’s many years 
ago. The Cardiff off-shore dock, the first of that type, was 
constructed in a shallow basin from which the water was ex¬ 
cluded for the purpose by a bank forming a dam, which was 
removed for launching purposes. 

No doubt the method has much to commend it,, and it would 
be interesting to know from the author whether the Mary¬ 
land Steel Company contemplates building ships upon the 
same berth, or whether the basin is intended for floating-dock 
construction only. 

It would also be interesting to know the cost of the dock 
when leaving the builders; the cost of preparing the basin in 
which it was constructed, including removing and replacing 
the dam; and how the cost of the latter was apportioned. 

As far as can be gathered from the small-scale drawing 
accompanying the paper, the author appears to have adopted 
the same arrangement of pipes as that used in the Clark & 


FLOATING DRYDOCKS. 


235 


Standfield docks. Although this arrangement appears to have 
become a standard, it seems questionable whether pipe arrange¬ 
ments could not be considerably modified in the case of two- 
sided docks, and it would be worth while to consider this seri¬ 
ously in future designs. 

As regards the surging experienced when sinking one of 
the pontoons for self-docking purposes, this is probably due 
to want of sufficient end-controlling power to cope with the 
natural tendency to dip whichever way it receives encourage¬ 
ment. It is just possible that at the time of submerging - the 
dock, the structure was riding upon air compressed under the 
deck due to the mouth of the air-pipe being shut off by the ris¬ 
ing water inside the tanks. Why one section should behave 
■differently from the other, it is difficult to say, but it might 
be explained by the position of the mooring chains, coupled 
with the tide being in an opposite direction, making it difficult 
to control them. 

As one who received his early training in the works and 
offices of Messrs. Clark & Standfield, under the late Mr. Lati¬ 
mer Clark and Mr. John Standfield, founders of the firm which 
bears their names, and, moreover, having taken a deep inter¬ 
est in the development of floating docks, the writer is able, 
from personal observation, to endorse all that Mr. Cox has 
said respecting Mr. Lyonel Clark. There can be no doubt 
that, showing considerable enterprise, Mr. Clark has done 
much to develop this particular branch of the profession. 

B. C. Laws, Eso.* (by letter).—The writer would like to 
add his tribute of praise for the very able and exhaustive man¬ 
ner in which the author has treated the subject, not only from 
the general standpoint, but more especially from that of design ; 
and it is mainly with regard to the latter that a few remarks 
will be made. 

The writer can hardly understand why the commercial ship¬ 
owner—as the author states—would prefer the floating dock 
on account of its flexibility. Vessels are and should be built 
without either hog or sag, that is, with a straight keel, and, 


* Associate Member, Institution of Civil Engineers. 






236 


FLOATING DRYDOCKS. 


under this condition, the best dock would be one in which that 
straightness would be preserved. But, if a vessel with a 
sagged keel were to be placed on the blocks of a dock de¬ 
signed for a certain maximum deflection, it would not be diffi¬ 
cult to conceive that the deflection due to the weight of the 
vessel might be so augmented by the natural sag of the keel 
that the maximum (safe) deflection allowed might be ex¬ 
ceeded, so that the dock would become permanently strained. 
Of course, the dockmaster, if he were cognizant of this peculi¬ 
arity in the vessel, would guard against such a contingency 
by ballasting the dock properly, but this information is not 
generally obtainable. 

This—perhaps not very important—objection to the floating 
dock is minimized by the assumption of flexibility in the vessel 
itself, so that—more or less—it will accommodate itself to the 
flexibility of the dock. However, it is just the uncertainty 
as to the extent to which a vessel is capable of bending that 
renders the problem of dock designing so difficult; and the 
general assumption that both the vessel and dock are flexible 
and bend together is perhaps the only reasonable one to make. 

The one great advantage of the floating over the ordinary 
graving dock is unquestionably the facility with which the 
operation of painting and repairs can be carried out, due 
mainly to the supply of light, and the ease with which material 
can be put on the deck. In this respect probably the L or 
single-wall dock has an advantage even over the double-wall 
type. 

With regard to the design, generally, it would have been 
advantageous in checking some of the data in the paper had 
the author given even a skeleton idea of the distribution of 
the weight of the dock. 

In the absence of this information, such a distribution might 
be assumed, as follows: 


Weight of wall and equipment X 2 = 1,750X2 = 3,500 tons. 
Weight of dock bottom or pontoon.= 7,900 tons. 

Total weight of dock.= 11,400 tons. 





FLOATING DRYDOCKS. 


237 


These weights may be assumed to be distributed in the 
usual way, both transversely and longitudinally, in the sides 
<md pontoon, respectively. Taking the length of the walls as 
4/6 feet, and assuming that the various transverse girders 
carry the weight of the walls, then, by considering any one 
girder, the passive forces due to the weight of the structure 
alone are: 


(a) 


n 3,500 8 

• P= - X—^=29 tons, 

2 476 7 ’ 


which may be assumed to act at a distance of 7 feet from the 
outer faces of the walls. 


<*) 


x A = 126 tons, 
1 500 


uniformly distributed along each girder. 

Together with the foregoing, there are also the active forces 
due to the load and buoyancy, which, on the assumption of 
distribution stated by the author, give: 

(c) ... .A total concentrated load on each girder = 400 tons. 

(d) .... A uniformly distributed upward ,force on each girder 

due to buoyancy = 0 X 8 = 500 tons. 

^300 

To this must be added the balance of 3,950 tons of water 
(about 2 feet deep) for the assumed freeboard of 2 feet. Of 
this, the weight borne by each girder = 63.2 (says 63) tons, 
uniformlv distributed. 



29 Tons 


Fig. 22. 































238 


FLOATING DRYDOCKS. 


The whole of the forces are indicated in Fig. 22. Sum¬ 
marized, these forces are: 

Downward forces: 

Due to weight of dock walls = 2 X 29 = 58 tons. 

Due to weight of dock bottom.=126 tons. 

Due to weight of contained water.= 63 tons. 

Due to weight of vessel.= 400 tons. 

Total = 647 tons. 

Upward forces: 

Due to buoyancy of water.— 500 tons. 


Balance (downward) = 147 tons. 

This means that, if the assumption that the weight of the 
vessel distributed uniformly over the 360 feet of keel blocks be 
correct, then there will be an upward supporting force of 147 
tons, to account for which, it may reasonably be assumed to 
be supplied by the walls, so that an upward force of 73.5 tons 
acting at 7 feet from the outer wall faces has to be included 
in the calculation for strength of the transverse girders. 

All these forces, collectively, give a maximum bending 
moment (at the center of the girder), as follows: 

(j)—When the vessel rests on the keel and bilge blocks 

= + 3.3 8 7 ft-tons. 

(2) —When the vessel rests on the bilge blocks only 

= + 1,162 ft-tons. 

(3) —When the vessel rests on the keel blocks only 

— + 7,887 ft-tons. 

Using the positive sign with the ordinary meaning, and assum¬ 
ing that the bilge blocks are situated so that they support the 
vessel at 33.5 feet from the center line—a reasonable figure for 
a warship of the displacement given—the foregoing values for 
the bending moment may be read from the diagram, Fig. 23, 
in which the bending moment curve, A, for the resultant load 
due to buoyancy and the other uniformly distributed loads, is 
superposed on the bending moment diagram for the three sys¬ 
tems of concentrated loading indicated above; and the result- 









FLOATING DRYDOCKS. 


239 



DIAGRAM OF BENDING MOMENTS FOR TRANSVERSE GIRDERS. 

_ Horizontal Scale _ 

0 10 20 30 40 ft. 

Vertical Scale 

r -1- 1-i-1 

0 1000 2000 3000 4000 ft-tons 

Fig. 23. 

ant bending moments for the entire loading are read off above 
the curve, A. 

The values thus determined differ from those given by the 
author, inasmuch as the latter were obtained without reference 
to the weight of the dock itself, or of the contained water; 
probably, however, a calculation was made including these 
items, and, if the author could state the results obtained, it 
would add to the value of the paper. 

Upon the same assumption of loading, the deflections of the 
transverse girders have also been determined, the concen- 

























240 


FLOATING DRYDOCKS. 


trated (downward) load being 400 tons, disposed in the three 
different ways already cited, and a resultant uniformly dis¬ 
tributed (upward) load of 311 tons. 

The formulas used were: 


(Oi) . . . . For a concentrated load, W ; 
taking the origin at that point on the de¬ 
flection curve in the line of action of W : 




Deflection = T — 

EI\ 2 



Pa '~ QP 
$EI(a + b) 


(bx) .... For a uniformly distributed load of intensity = w 
tons per foot run, taking the origin on the deflection curve on 
the center line of the girder. 


that is, 

where 


> 

■ tttf-- 

= 311 tons 



«- 67 -- 

- ->■ 


Deflection 


W I r 79 , X* I^X 1 

I Llx 2 + — — —— n 


2 El 


12 


y 


,, 21 I X X 1 X I 2 3 / 0 r\ 

? = Lx 268 xei ( ^~ 2i ' 3o6) ’ 


o i x 

L = 67 feet; / = 7 feet and w — —— tons. 

134 


The deflection curves are shown in Fig. 24, from which the 
resultant maximum deflection—at the center of the girder— 
may be obtained as follows: 

Where E — 15,000, and I = 1,045,000. 

(1) . .Vessel resting on the keel and bilge blocks = + 0.51 in. 

( 2 ) . .Vessel resting on the bilge blocks only. . . = + 0.3 in. 

(3) . .Vessel resting on the keel blocks only. . . = + 0.89 in. 

These deflections should be reckoned for a length of 120 feet. 

The amount specified, viz., 1 in 2,000, gives 0.72 inch for this 
length, a value less by a small amount than the maximum ob¬ 
tained by calculation according to the third condition above. 
















FLOATING DRYDOCKS. 


24I 


DIAGRAM OF DEFLECTIONS FOR TRANSVERSE GIRDERS.. 

A Deflections due to vessel supported on keel and Bilge blocks, only. 

B “ “ “ “ “ “ “ “ Bilge blocks, “ 

C “ “ “ “ “ “ keel blocks, only. 

D “ • “ “ Buoyancy and other uniformly distributed loads, only. 

m E Resultant Deflections due to all loads, collectively. 

Horizontal Scale of feet 

o" - 


10 


To 30 40 60 

Vertical Scale of inches 

0 ^ 


60 


~i-1 

70 80 


1 r-| 1 i 1 r 1 1 ' 1 I ]—I—| 

X X X 2 



Fig. 24. 


It is not likely, however, that such a heavy vessel as the one 
chosen would, in practice, ever be supported on the keel blocks 
alone, but would be sustained at the bilges, more or less, a 
case approaching the first condition. 

16 



























































242 


FLOATING DRYDOCKS. 


With reference to the skin plating, it would seem reason¬ 
able to treat it—with some modification—as a continuous beam 
bearing on broad-surfaced supports and fixed at regular inter¬ 
vals of 24 inches by riveting at the frames. 

If a 1-inch strip of the plating between any two consecutive 
frames is treated as an elementary beam of length equal to the 
frame spacing, i. e., from center of flange to center of flange, 
and if it be assumed that the plating between the line of 
rivets and the edges of the frame flange has no curvature, then 
it may be considered that the pressure over the supports varies 
uniformly from zero at a or b —the ends of the beam—to a 
maximum at the bearing edges, c or d, Fig. 25, and the re¬ 
sultant pressure or reaction will act through a point distant 
one-third of a c or b d, from c or d, respectively, and the dis¬ 
tance between these points may be taken as the virtual length of 
the beam to be used in the calculation, viz., 22\ inches for 
a 3J4-inch flange. This would mean that there is no outward 
pull on the rivets due to the bending of the plate over the sup¬ 
ports, a condition which, probably, is only realized approxi¬ 
mately in practice. 



The law governing the distribution of pressure over the 
bearing surface, as d b, is generally unknown, and may be rep¬ 
resented by a curve such as b f, on Fig. 26, the ordinates of 
which at any point represent the pressure at that point. The 
assumption of uniform varying pressure, however, is probably 
not far from the truth, when the curve would become the 
straight line, b f u whereof the area, b d f, is equal to the area, 
b d f u and the resultant pressure which will always act through 
the center of gravity o,f the area of the pressure curve cuts 


d b, at (or about) a distance of 


d b 


from d. 


3 







FLOATING DRYDOCKS. 


243 


If, however, the rivets experience an outward pull, the curve 
of pi essui e will be of the nature of c f, Fig - . 27, where b 6 
denotes that pull, and the pressure on the support will only 
extend over the distance, d g. 




The hydrostatic pressure on the plating will be resisted partly 
by the stresses due to bending and partly by those due to the 
stretching of the plate; and if p denotes the intensity of stress 
due to bending only, and q denotes the intensity of stress due 
to tension only, in consequence of the beam when bent being 
longer than when straight, then both p and q should strictly 
be used in determining the thickness of the plating. 

Theoretically, however, the formulas connecting p and q are 
very complicated and too unwieldy for practical use; they are 
built up on assumptions which are not altogether trustworthy, 
and, even when used in the calculation, the results obtained 
differ by only a small margin ifrom those obtained by using for¬ 
mulas derived in a more simple way. The best assumption to 
make is that the ends remain undeflected when the beam bends 
under the load put upon it, when the latter may be regarded as 
equivalent to one span in a continuous beam of an indefinite 
number of equal spans; the “theorem of three moments’’ may 
then be applied, and the reasoning is parallel with that relating 
to the encastre beam, in which case the distance between the 
edges of the support would be 21 inches. This, however, would 











244 


FLOATING DRYDOCKS. 


give a result for the value of the stress less than what is prob¬ 
ably realized, whereas the length of 24 inches would give too 
great a value; hence the reason for taking 22\ inches as the 
length for purposes of calculation, as explained above. 

In the encastre beam, the maximum value of the bending 
moment occurs at the edge of the support (and is twice that 
at the center of span), and the thickness of the plating will be 
given by the formula: 



where w is the uniform load intensity, and k is the stress inten¬ 
sity in the material. 

Converting w into terms of H , the head of water, 

/= p/zr 

\ 10,322 k 

which, making L = 22^ inches, H — 35 feet and k = 4.46 

tons, gives a value of t — 0.611 inches = g 5 inches ; slightly 

greater than that obtained by the author. 

Values obtained by this formula produce a curve which 
agrees fairly well with that obtained with Bach’s iformula, but 
it falls below the fixed-beam formula, Curve e of Fig. 28. 



(e) Fixed-beam formula: t 2 = 0.0001 ~-~ 

(d) Rectangular plate formula (Bach): t 2 = 0.468 w a? b 2 +- k (a* + b 2 ) 
(£) Formula: t 2 *=/f L 10322 fc, where L is as defined above. 


Fig. 28. 






















FLOATING DRVDOCKS. 


245 


Space will hardly permit of a survey of the design of other 
portions of the structure, notably the walls of the dock, which 
form practically in themselves the longitudinal strength of the 
structure. The author, apparently, calculates this latter with¬ 
out any reference whatever to the vessel docked; some design¬ 
ers, however—on the assumption that the dock and vessel bend 
together in concert—allow a margin of strength on account of 
the aid rendered by the vessel to the longitudinal strength Ojf 
the combined structures. The author’s method is perhaps the 
best one to adopt, and, if it errs at all, it does so on the side 
of safety. 

The stability of the dock forms one of the most interesting 
features of the design, and is indeed of the utmost importance, 
since upon it depends the safety of the vessel when docked. 
Any tendency of the dock to move away from the upright posi¬ 
tion, due to wind pressure or other causes, would at once bring 
unknown forces to bear on the supports, and, through them, 
on the structure of the dock itself, to the possible detriment of 
the latter, and disaster to the vessel. 

The three important cases to consider are: 

1. —When the vessel takes the blocks; 

2. —When the keel just becomes emerged; and 

3. —From the time of emergence of the keel until the deck 

of the dock becomes awash. 

These points have been set out clearly in the diagram given 
by the author. 

It is rather surprising, however, to find the curve of metacen- 
tric height showing so large a value at the deep draughts such 
as the E water line as compared with that indicated at the 
smaller draughts at C or B, but, in the absence of sufficient 
data, it is not possible to check the diagram. 

The critical points referred to by the author are presumably 
those at the C (top of blocks) water line and the inner three 
points at the B (deck of pontoon) water line. Why the desig¬ 
nation “critical” should be given to these points or to the 
period of time between C and B is not quite clear. 

It is true that, with the dock lifting, the system loses the 





246 


FLOATING DRYDOCKS. 


influence of the vessel as regards its stability, but, clown to C, 
this influence has diminished gradually, and there is no sudden 
break in the curve at C, so that, if the stability is good for 
points above the level of C, it will be satisfactory also for points 
below C, until, when the deck emerges, there is a sudden and 
large increase in the value of the stability. 

This is made more clear by the consideration of the fact 
that, with the pumping out of the water, the center of gravity 
of the system is continually increasing its distance above (say) 
the bottom of the dock, while the height of the center of buoy¬ 
ancy is diminishing; but the increase in distance between these 
two points is seldom greater than the increase in the value of 
the bending moment. 

L. J. Le Conte, M. Am. Soc. C. E. (by letter).—The long 
and eventful voyage of the floating dock Dewey to Manila Har¬ 
bor, covering a total distance of some 16,000 miles, will always 
be remembered with admiration by harbor engineers the world 
over. It was a great feat, well performed. It is not necessary 
to state that repair docks, of whatever type selected, constitute 
an important part of the necessary equipment of every sea¬ 
port. The cleaning of barnacles, sea grass and other marine 
growth from a ship's bottom, after a long voyage, is always 
necessary if it is cared to maintain her speed. In the case of 
the smaller vessels, this may possibly be done on suitable tide 
flats, or on marine railways; but, in the case of all large ves¬ 
sels, and even for extensive repairs on smaller vessels, drydocks, 
floating docks, or lift docks become an absolute necessity. At 
least one dock in every port should be sufficiently long, of 
ample width, and deep enough to accommodate the largest ves¬ 
sel coming into that port. For convenience, it would probably 
be well enough to have in such a dock an intermediate gate 
seat to accommodate smaller vessels. 

A good, sheltered harbor, properly developed and well sup¬ 
plied with internal railway communication, together with ample 
facilities for cheap, rapid and reliable repairs to vessels, also 
with facilities for the rapid dispatch of cargoes, both in load¬ 
ing and discharging, will certainly benefit, not only the natural 


FLOATING DRYDOCKS. 


247 


trade o-f the port, but also, what is most important, tend to 
make the harbor a port of call for a widely extended trade. Of 
•course, the lower the harbor dues, the more inducements there 
will be for vessels to use the port, and sometimes the authori¬ 
ties in charge will find it to their advantage to make the port 
entirely free, and charge dues only for services actually ren¬ 
dered, such as pilotage and cranage, with possibly some very 
small amount for the maintenance of the docks. 

A few years ago timber drydocks were in great favor on 
account of their cheapness and the rapidity with which they 
could be built, say, in four years. Long and varied experience, 
however, has developed the necessity of inordinate expenses 
to meet annual repairs and maintenance. This, of course, takes 
away greatly from the usefulness of such structures, and rele¬ 
gates them to the class where they properly belong, namely, to 
temporary structures. 

Now comes the steel floating dock, of 20,000 tons capacity, 
which can be built complete and ready for active sendee in 23 
months. The cost is somewhere between that of the timber 
dock and that of the old style of granite dock. This puts the 
whole question in a new light, and adds much to its economic 
value. 

Seafaring men, as a class, are very conservative, too much so 
for their own good, and they do not care to try anything that 
has not already gone through the test of widespread experience. 
This trait is highly commendable, if not carried so far as to 
destroy an officer’s usefulness in the service. He should al¬ 
ways be on the alert to pick up quickly any important improve¬ 
ment, and be able to analyze the true scope of its bearings on 
other features. Very few men have this faculty. 

Every new project, no matter how well conceived, developed 
and carefully studied out in all its details, is always met by an 
endless chain of objections. Practically speaking, objections 
really have little weight unless it can be proved that they have 
some financial value. Hence the size of any objection, aftei all, 
is generally measured in the financial scale. When this test is 
favorable, the remaining objections soon disappear. I herefoi e, 


248 


FLOATING DRYDOCKS. 


from a financial point of view, everything seems to be in favor 
of the steel floating dock. From a strategic point of view, it 
has great advantages in its complete mobility. Again, it pos¬ 
sesses the invaluable feature that, in cases of emergency, the 
depth of water available over the keel blocks can be increased, 
at will, to 37 feet or more, to accommodate vessels in distress, 
which naturally draw more water than usual when on an even 
keel. It seems to the writer that everything points strongly to 
the steel floating dock as the coming style of future harbor 
works, as it has so many important intrinsic advantages. Sec¬ 
tional docks are certainly a great improvement on the old style, 
as they permit of self-docking, a most important requisite. The 
Maryland Steel Company’s type really leaves very little more to 
be desired. 

All new docks should have an available depth of at least 40 
feet on the sill, at high water of spring tides, and a total length 
of from 900 to 1,000 feet. This is not too large, taking into 
consideration the rapid growth in the size and draught of ves¬ 
sels. 

W. H. Pretty, Esq.* (by letter).—The writer has exam¬ 
ined this paper with much interest. The author does well to 
emphasize the need of more and suitable repair docks of the 
graving or floating type to meet the requirements of the world’s 
shipping. Their value, in time of peace or war, cannot be over¬ 
estimated in the development and defence of the commerce of 
any country. The mobility of the floating dock, and the fact 
that it can be constructed at a convenient economic base and 
towed to its destination, ready for immediate use, are condi¬ 
tions greatly favoring this type of dock; and when, combined 
with this, one considers the ease with which it can be put out 
of action, temporarily or finally, to prevent it from falling into 
the hands of a powerful enemy, it is not without strategical im¬ 
portance. 

In the historic portion of the paper, Mr. Cox has not men¬ 
tioned a certain useful type of graving dock, in which the 
natural fall of a river, a rapid, or a tidal difference Ojf level is 

•Associate Member, Institution of Civil Engineers. 




FLOATING DRYDOCKS. 


2 49 


utilized, the available supply of water being used to dock ship, 
and the natural fall to a lower level to drain the dock, no 
pumping machinery being used. A few small docks of this 
class, and apparently of ancient date, existed in Cardiff, some 
years ago. It may not be without interest to mention here 
that in the Village of Willington, Bedfordshire, England, on 
the River Ouse, about 4 miles from Bedford, there exists, in 
a good state of preservation, the remains of a Danish camp 
and dockyard, presumably a repairing yard. 

It does not follow that there is always more water to pump 
from a “graving” dock, for, in the case of a ship absolutely 
fitting the dock, there is no water to pump out—this is the 
analogue of Lewis Carroll’s “bath” in a minimum quantity 
of water. In a floating dock of the same lifting capacity, 
under similar conditions, the whole of the water correspond¬ 
ing to the displacement of the dock and ship, or the “maxi¬ 
mum load, will have to be dealt with by the pump. 

The elastic deck of a floating dock is unquestionably a valu¬ 
able feature, from a shipowner’s or underwriter’s point of 
view, and might be copied, in principle, in the construction 
of the floors of graving docks, with advantage to the vessels 
docked therein. 

It is interesting and satisfactory to notice that the value of 
docking keels, or virtually “three lines of keel blocks” was 
recognized in the construction of the Dewey dock, and it is to 
be hoped that all vessels, in the near future, will be designed 
to meet this method of docking; it seems almost barbarous, 
even to think, that vessels should be now designed for dock¬ 
ing on any other plan, and to see a large warship going 
through the old-fashioned process of shoring on a floating 
dock gives food for much thought, while the time thus lost 
is of the utmost importance, to say nothing of the risk to 
the 800 or more souls on board. On the other hand, one is 
tempted to ask for a few more data as to the distribution of 
pressures, and the means taken to allow the vessel to bed 
herself without excessive stress in any place. Something is 
known of the distribution of stresses when on a single line 
of keel blocks. 


250 


FLOATING DRYDOCKS. 




It should not be forgotten that a timber drydock can be 
destroyed more readily than a masonry structure in time of 
war, should such a course become necessary. 

There is no question that all floating docks should be self¬ 
docking; the best means of doing this, however, is still a de¬ 
batable question. The plan adopted for the Dewey is excel¬ 
lent, but the design of the end pontoons does not appear to the 
writer to be by any means ideal, although the general scheme 
is good. The watertight freeboard should always be sufficient, 
and distributed so as to guarantee absolute control in sinking 
or raising the section under manipulation; but, if the writer 
understands Fig. 20 correctly, this does not seem to have been 
done. 

In painting the surface of steel structures generally, suffi¬ 
cient importance is not attached to freedom from moisture in 
the paint used, or the absence of water or moisture blisters 
between the clean metal and the outer surface or film of paint, 
often introduced by unskilful laborers, it being a general im¬ 
pression that anyone can use a paint brush. 

The author’s comparison of graving and floating docks, on 
page 158, is open to criticism, in the particular case in ques¬ 
tion. When docking a small ship in a graving dock, she can 
be run over the sill at a comparatively low draught on a rising 
tide, and only the water thus admitted need be dealt with, 
whereas, in the case of the floating dock, the minimum weight 
to be dealt with is that of the dock plus the ship. 

The only fair way of comparing the work done in pumping 
during docking ship, in graving and floating docks, is by 
electrically-driven plant, when the whole record o ; f kilowatt- 
hours would tell the story, the real question at issue with 
respect to the pumping plant in docking ship is the total energy 
in foot-pounds, foot-tons, or kilowatt-hours (say) consumed 
from the moment the ship touches the blocks, to the deck or 
floor awash in floating and graving dock, respectively. There 
is no excuse for the non-introduction of electricallv-driven 

w 

pumps, either in graving or floating docks, while this form of 
energy can be utilized for all purposes; and a central station 






FLOATING DRYDOCKS. 


2 5 r 


on a floating- dock would place all the pumps under one con¬ 
trolling center, not even excluding the independent clocking 
sections, which could be fed by special cables. 

It would add greatly to the value of the paper if a plan 
and section of the No. 4 drydock (mentioned on page 159 
\\ ei e given, to enable a calculation to be made for compari¬ 
son with the figures shown. The writer would ask Mr. Cox 
to confirm these figures, particularly the 58,700 tons of water 
which, it is understood, are to be removed below the level of 
the top of the blocks. From a rough estimate, the writer 
w ould expect this graving dock to be capable of dealing with 
a 25,000 to 30,000-ton ship. 

In reference to the remarks on page 163, a disabled or leaky 
ship very frequently has a list, and it is probable that sec¬ 
tional docks, in which one section can be detached, floated 
under the ship and then have its buoyancy added to assist the 
disabled portion, would do more good for temporary assist¬ 
ance, or say, “first aid.” It would be interesting to have 
some records of ships with a list docked in floating docks. On 
the other hand, the value of a floating dock for deep-draught 
vessels is unquestionable. 

The method of self-clocking adopted in the Dewey is ingen¬ 
ious and simple, and possesses considerable merit. Plate 
XXIII conveys the impression that the side walls are undercut 
outside below the dock level, while the letter press appears to 
indicate that the side walls are continued vertically downward 
outside to the level of the keel plates of the dock. The writer 
would like Mr. Cox to explain this a little further. The solid- 
trough dock, although stronger, might be less valuable in time 
of war than a sectional dock, particularly in dealing with 
torpedo-boat destroyers or submarines. 

The specification of steel on page 178 should state a definite 
ratio of measured length to diameter in measuring the elon¬ 
gation, and in the case of other forms of section, an equivalent 
ratio of length to sectional area should be stated, otherwise 
the firm possessing the most powerful testing machine will 
score. Flat steel plates should be bent, cold, 180° in and also 


252 


FLOATING DRYDOCKS. 


at right angles to the direction of rolling, or, “with the grainU 
and “against the grain/’ as it is sometimes expressed. 

The provision of 12 inches of water in the bottom of a pon¬ 
toon dock when the ship is docked is wise, as it gives some 
little control over the pumping operation toward the end of 
the pumping. In the writer's opinion, the depth should be in¬ 
creased for docks used in choppy seas, as any surging tends 
to uncover the suction pipes, and the nearest pump may lose 
its water, and race away. Under ideal conditions this trouble 
does not arise, but in the absence of suitable gauges for indi¬ 
cating the depth of water in the various pontoons, a depth of 
water sufficient to guarantee the suction pipes against drawing" 
air, with reasonable attention at the pumps, should be allowed 
for. There does not seem to be any description of a water- 
level indicator, or of an air inlet, but presumably these were 
used. 

Leonard M. Cox, M. Am. Soc. C. E. (by letter).—All who 
are interested in the subject must highly regard opinions based 
upon the experience of Mr. George B. Rennie, the dean of 
floating-dock designers. His discussion has historic value, and 
it is especially interesting to note that, notwithstanding the 
numerous devices proposed for self-docking floating docks, the 
apparent tendency today is to return to the solid one-piece type 
represented by Mr. Rennie’s Cartagena dock. 

Mr. Baterden’s fair discussion of the relative merits of the 
two types of docks under varying conditions, seems to call for 
some explanation on the part of the writer. While confining 
itself generally to the subject of floating docks, with special 
reference to the design and construction of a particular struc¬ 
ture, the paper has failed to attain the object for which it was 
written if it stands as an argument in favor of floating docks, 
as opposed to graving docks, for any and all situations and 
requirements. On the contrary, a frank discussion was at¬ 
tempted on the idea that “each type has its own particular field 
of usefulness which the other cannot with advantage fill, and 
that, for a given set of conditions, a careful study of both 
types, as applied to the special requirements of the case, must 







FLOATING DRYDOCKS. 


253 


govern the choice.” This, it would appear, is Mr. Bater- 
den s position, while admitting a bias in favor of the drydock 
in the majority of instances. 

It was not the intention to state as a general law that the 
cost of a graving dock is greater than the cost of floating dock, 
but that, foi equal capacity and in situations equally favorable 
or unfavorable to each type, the floating dock “costs about the 
same, and in some instances less.” Table 1 is unsatisfactory 
in that it fails to give the cost, completed, of three of the new 
docks. These data were not available at the time the paper 
was written, but it has since been learned that the total costs 
of the New Charleston and Norfolk docks are $1,085,273.00 
and $1,201,347.82, respectively, the former less and the latter 
more than the cost of the Dewey. The new docks at League 
Island and Mare Island yards exceed the Dezvey in first cost, 
while no estimate of the completed cost of No. 4 Dock, New 
York, can be made. The new dock at Boston cost $1,105,- 
000.00, or $19,000.00 less than the Dezvey. The Dezvey at the 
site and on the date of the official trials cost $1,143,959.68, of 
which amount all above the contract price, $1,124,000.00-, was 
expended for very desirable though not absolutely necessary 
improvements, such as compressed-air plant, bitumastic enamel 
paint for pontoon bottoms, etc. 

While on the subject of comparative costs, it may not be 
amiss to point out the fact that the 20,000-ton battleships, so 
the writer has been informed, will have a beam of about 85 
feet 2^ inches, and a length of 518 feet over all. The Dezvey 
can easily dock these ships with 7 feet clearance between the 
sides of the ship and the painting stages. Table 4 gives the 
docking capacity of the only United States docks capable of 
admitting ships of this size, and it will be noted that only two 
of the docks listed are now completed. 

The writer agrees with Mr. Baterden in the opinion that 
the floating dock is not suitable for locations requiring exten¬ 
sive dredging with periodical re-dredging, unless other con¬ 
siderations warrant the necessary additional expense both in 
first cost and in maintenance. 


254 


FLOATING DRYDOCKS 


TABLE 4 . —Docking Capacity of Largest Naval Docks. 


Dock. 

Draught over 
sill, M. H. VV. 

Maximum ship. 

Remarks. 

Length, 
over all. 

Beam, 
in feet. 

Portsmouth No. 2.. 

ft . in. 

30 0 

3 ° 75 

31 0 

30 0 

34 0 

34 0 

30 0 

38 0 

ft. in. 

728 9 

727 O 

518 9 

729 10 

529 8 

554 0 

726 4 

655 0 

86 

86 

88 

86 

96 

96 

86 

98 / 

Completed 1906. 
Completed 1906. 
Under constr. 
Nearly complete. 
Under constr. 
Under constr. 
Nearly complete. 
Construction not 
yet begun. 

Boston No. 2... 

New York No. 4. 

League Island No. 2. 

Norfolk No. 3. . 

Charleston No. 1. 

Mare Island No. 2. 

Puget Sound No. 2. 



Noth. —A clearance of 2^ feet has been allowed forward to head of dock and 2% feet aft to over¬ 
hang of caisson. Maximum length of ships has been taken on line 15 feet above bottom of keel. At 
the entrance, net clearance 4 feet each side at M. H. W., ship drawing 29 feet. New ships (20,000- 
ton), to be approximately 5x8 feet over all, have 85 feet 2*4 inches draught; 27 feet normal and 29 
feet 3 inches maximum. 


The high range of tides existing on the coast of Europe and 
the British Isles does not obtain in America, and was not con¬ 
sidered in the comparison of pumping* required for each type 
of dock. Such a condition would undoubtedly affect the quan¬ 
tity of water to be pumped, in the case of the graving dock, 
yet, even under the most favorable circumstances, considering 
the variation in the size of the ships docked, the average pump¬ 
ing expense for a definite period of time would, in the writer’s 
opinion, be appreciably less for the floating structure. 

For naval purposes, the advantage of the quality of mobility 
would be valued more in times of war than in times of peace. 
At such times the matter of towing expense or the cost of an¬ 
cillary structures, should such be necessary, might be ignored 
in view of the strategic importance of a required move. For 
commercial purposes, it is not proposed that floating docks be 
moved at all, except for weighty reasons; such, for instance, as 
an entire change of plant location, impending danger from 
water-front conflagrations, or other equally important consid¬ 
erations. The necessity for moving the dock would evidently 
occur infrequently, but, if it occurred once during its lifetime, 
its mobility might be the means of increasing the possible 
earnings, or even saving entirely a large investment. 

Mr. Peabody very justly criticises the unfortunate obscurity 





























FLOATING DRYDOCKS. 


2 55 


of certain parts of the calculations. It should have been stated 
on page 184 that the position of the bilge blocks was assumed 
from the preliminary design of the 16,000-ton class battleships. 
As Mr. Peabody infers, they were spaced 22 feet from the keel 
blocks. The limits of a paper of this kind make it necessary 
to omit much that might be of interest, and tempt the writer 
to geneial statements of methods rather than detailed com¬ 
putations. This may account for the omission of the calcula¬ 
tions for stability with ship 1 foot off center, as well as the 
stability under the specified wind. As Mr. Peabody has 
remedied the defect as regards the former, and as the general 
method for obtaining the latter is indicated in the paper, they 
will be omitted from this discussion. 

The value of such a paper as the one referred to by Mr. Pea¬ 
body (Boobnoff’s “Stresses in a Ship’s Bottom Plating Due 
to Water Pressure”) is undeniably great, and it may yet be 
the means of assuring to the profession an easily handled 
tool; but it is not too much to say that the computations con¬ 
tained therein will hardly come into general practical use in 
their present form. The results of the experimental work of 
Captain Hovgaard, of the Massachusetts Institute of Tech- 
nology will doubtless prove of great value, judging by the 
thesis of Assistant Naval Constructor Ferguson, U. S. N., 
presumably referred to by Mr. Peabody. The ordinary proce¬ 
dure, of consulting Lloyd’s or other Marine Underwriters’ 
tables of scantlings, is the simplest and possibly the best way 
at present of determining detailed dimensions, but the great 
stumbling block to their use, from the standpoint of the engi¬ 
neer, is that he is not always able to discover just how their 
results were obtained. Few of us can use formulas or tabu¬ 
lated results without having a clear idea of their derivation or 
source. 

If, as Mr. Colson points out, “it appears desirable that the 
power of docking at full-load draught at low water of spring 
tides should be available,” would not the requirement greatly 
increase the cost of a graving dock in localities where, as in 
the British Isles, the range of tide is great? It is admitted 


256 


FLOATING DRYDOCKS. 


that the same objection would hold for floating docks if deep 
water near shore is not available, but, given the depth of 
water, the floating dock is the obvious solution of the prob¬ 
lem. 

The writer agrees with Mr. Colson that one of the weakest 
points of the floating structure is the difficulty of handling 
heavy weights from the side walls. This problem will doubt¬ 
less be solved, but, up to the present time, no satisfactory 
arrangement for heavy deck cranes has been evolved, owing to 
the interference with lines, stacks, guys and general deck 
gear. As regards fire, it is conceivable that a ship in drydock 
might be seriously threatened by burning shop buildings, 
whereas in a floating dock on the water front it would be out 
of danger, or if in danger, could be saved either by sinking 
the dock and moving the ship, or moving the dock and ship 
together. 

The cost of preparing berth, shore connections and perma¬ 
nent moorings of the Algiers floating dock was included in 
the contract price. The cost of the same work for the Dewey 
cannot now be given, as permanent plans will depend upon 
the final arrangement of the naval station at Olongapo Or 
Cavite. 

While actual cases of a heavy battleship being docked with 
a list, by trimming the pontoon to accommodate the list, 
are not known, the Algiers dock has successfully performed 
the operation with commercial vessels, and, in a similar man¬ 
ner, a careful dockmaster should be able to dock a warship 
by bringing his dock back to an even keel shortly after the 
ship takes the blocks and before it has lost much water sup¬ 
port. Of course, there would be a limit to the amount of list 
that could be taken out in this way, but, even thus limited, 
circumstances can be imagined which would make this a valu¬ 
able quality in a dock. 

Mr. Cunningham points out a new use for the floating dock, 
which, from a naval standpoint, would seem to be a most 
important one. The possibilities of the floating dock as a dry- 
dock auxiliary should appeal strongly to legislators who have 



floating drydocks. 


257 


to do with appropriations for public works. If the Govern¬ 
ment must provide docks for the heaviest ships at abnormal 
di aughts, all the naval docks of the United States would 
eventually have to be enlarged or replaced at enormous cost, 
vv tile, since the heaviest ships are few in number and the con- 
c ltion of abnormal draught rare, every purpose would be an¬ 
swered by few large floating docks distributed at suitable 
points. 

The independent caisson proposed by Mr. Cunningham 
appears to meet the requirements of the case so fully that 
experiments with a large or full-sized model will be awaited 
with much interest. The supplemental chamber for the con- 
tiol of the buoyancy is novel. To avoid surging in submerg¬ 
ence, he would doubtless arrange the chamber or chambers so 

that the admission of water could be controlled for trim_an 

object easily accomplished. Could not this caisson be fitted 
with a movable deck for a working float, and on its tower 
have cranes installed with reach sufficient to handle heavy 
weights over the dock’s side wall when alongside? Also, 
could not such a caisson be designed for easy towing, that is, 
fitted with bow and stern in the direction of its length? If so, 
one such would answer all requirements for docks proposed for 
the Atlantic Coast, one for the Gulf and one for the Pacific. 
If, by the use of this device or some other, the objections to 
the solid dock can be overcome, the result will be a stronger 
and stiffer dock, and, what is equally important, increased con¬ 
fidence on the part of the dockmaster. 

Mr. Clark’s discussion of the question of skin plating 
brings out with greater clearness the point to which the writer 
desired to call attention in his paper, and he has endeavored 
to illustrate this by a comparison of actual examples of ship 
practice, in his reply to Mr. Laws. There is no doubt that the 
use of beam formulas for skin plating gives stresses largely 
exceeding any to which the material is ever actually sub¬ 
jected. As stated in the paper, the fact that beam formulas 
gave a "considerable excess of strength” was known and duly 
considered by the designers, but the extra thickness obtained 

17 


258 


FLOATING DRYDOCKS. 


by their use was considered desirable for other reasons. T he 
formation of a protecting marine growth before the thick¬ 
ness of metal is reduced to that absolutely necessary for the 
stress may be the means of effecting a saving in self-docking 
expense, besides insuring against neglect. Docks are not in- • 
tended to show speed qualities, therefore marine growths are 
of no particular detriment to steel bottoms except by reason of 
the added weight. 

There is also a general tendency in the United States to¬ 
ward the liberal use of material and large safety factors in 
anticipation of remote contingencies, which, in older and more 
heavily taxed countries, probably seems like extravagance, and 
in the future this may seem to be so here. As an indication 
of the wisdom of this policy, the case of the Havana dock may 
be cited. There were two years of the life of this dock during 
which it was badly neglected. The Spanish Government did 
not expect to retain it, and the United States had not deter¬ 
mined upon its purchase. When the matter of its purchase 
finally came up, a board of officers was ordered to examine and 
report upon its condition; it was found that in the foul waters 
of Havana Bay the plating had scaled to a depth of from 
to tV inch, all the under-water rivet‘heads had swelled and 
opened like chestnut burrs, and the whole under-water body 
had deteriorated. It was the opinion of the Board that the 
lifting capacity of the dock had been reduced from 10,000 to 
6,000 tons. Now, with an allowed unit stress of 13 tons per 
square inch, the formula for skin plating used in the dock cal¬ 
culations gives inch instead of the if inch thickness actually 
used. This leaves inch of extra metal, which exceeds by 
a very little the At inch of corrosion found in the Havana 
dock. 

As regards the “bolted sectional” dock of Messrs. Clark & 
Standfield, the writer readily admits the possibility of making a 
joint of a structure stronger than the body of the structure 
itself, but, considered merely as types, it would seem that the 
one-piece side walls with overhanging ends bearing on short 
end pontoons would be considered stronger than a dock com- 


FLOATING DRYDOCKS. 


2 59 


posed of square-cut sections joined to each other at their 
etges. Mr. Clark’s statement, that these sections are some¬ 
times riveted, would lead to the conclusion that frequent self- 
dockings are not contemplated. 

The inspection of the Havana dock, prior to its purchase, led 
to the recommendation that all connection bolts be placed 
above the normal water line, as under-water bolts caused much 
annoyance in self-docking, and could rarely be withdrawn in 
a usable condition. While it is true that the Dewey at the time 
of ^ ei ^ es ^ s was new and in good condition, it may be worth 
w hile to note that, in the self-docking operations, every bolt 
was withdrawn and re-inserted without the aid of mauls, and 
that not a bolt was lost. Besides the objection to them in 
self-docking under-water bolts must be a constant source of 
anxiety, since their condition after long immersion could 
never be ascertained with certainty. 

Though a docking deck only 12 feet in length would seem 
to be inadequate foi the seating of a long and heavy section, 
the fact that the pointed ends project some 50 feet farther 
under the lifted section removes doubt as to the possibility of 
safely self-docking the bolted sectional dock. It is understood 
that the existence of a basin dock at Pola capable of docking 
the sections will probably prevent a practical test of the self¬ 
docking features of the Pola bolted sectional dock. Experience 
with the Detroit dock, of the same type, and with the new docks 
mentioned by Mr. Clark, will be awaited with interest, and will 
doubtless remove many of the objections suggested by a mere 
consideration of the scheme on paper. 

Paragraph 42 of the specifications provides that, “Within the 
limits of allowed deflection the shipload shall be assumed to be 
perfectly flexible.” As limited, the assumption is substantially 
correct. Mr. Clark seems to interpret the term “flexible” as 
meaning flexible without elasticity, and to overlook entirely the 
limits of the assumption set forth in the specification. This 
assumption is made for bending and not for shear. As a crude 
illustration, it would take the slightest transverse pressure to 
deflect a taut string 1 inch, but a very appreciable force to 
deflect it 16 inches. 


26 o 


FLOATING DRYDOCKS. 


The uniform pumping clause in the specifications was in¬ 
serted to insure against clanger from unskilful operation. 
While the official tests required uniform pumping, it was not 
contemplated for ordinary docking operations, and an intelli¬ 
gent dockmaster would as surely regulate the buoyancy accord¬ 
ing to the loading as in any other type of dock. The square 
ends and uniform buoyancy permit the docking of a ship having 
a keel length equal to the length of the dock, and, as far as was 
learned from the voyage of the Algiers dock, the square bow 
detracts nothing from the towing qualities. 

Mr. Clark’s comparison of the deflections caused in H. M. S. 
Dominion and the U. S. S. Iowa, when docked in the Bermuda 
dock, and the Dewey, respectively, would have been of more 
value, had the length of those ships been given. The Naval 
Pocket Book of 1904 gives the length of the Dominion as 425 
feet, and that of the Iowa as 360 feet. In comparing the per¬ 
formances of the two docks, it should he borne in mind that, 
in the test of the Dezuey, the dock was raised by uniform pump¬ 
ing, and, furthermore, in order to allow for the difference in 
weight between the Iowa and the specified i6,ooo-ton ship, the 
dock was raised to a freeboard of 4*4 feet instead of 2 feet, as 
specified. During the docking, the exceedingly high tempera¬ 
ture which obtained was broken by a sudden rain of short du¬ 
ration ; these conditions gave quite a variation of temperature, 
and the deflection ranged from 1.8 inches to a maximum of 4 
inches. There is no doubt that temperature strains are induced 
under such conditions which might well warrant the low unit 
stresses adopted. The whole of the deflection could easily have 
been eliminated had it been permissible, under the regulations 
of the official tests, to use discretion in pumping. With the 
Dewey , as with the docks cited by Mr. Clark, it is quite easy to 
hog a slightly sagged ship by manipulation of the pumps and 
valves. 

Mr. Clark's objection to the trough or solid dock, namely, 
that there are locations where basins could not be built capable 
of holding the entire structure, would hardly hold good in 
many parts of the United States, though it might prove a 


floating drydocks. 


261 


serious obstacle abroad. Nevertheless, it would seem that 
broadside launching could be accomplished without extraordi¬ 
nary risk, and that in a country with a great range of tides, 
as in the British Isles, there would be few locations which 
would not offer some solution of the problem. At all events. 

it might be worth the trouble and extra expense to attempt the 
solution. 

The writer desires, in passing, to acknowledge his obliga¬ 
tion to Mr. Clark for his [frank discussion of the paper, and 
to expi ess the high estimation in which he holds any opinion 
given by that eminent engineer. 

Mr. Laws discussion of the question of transverse strength 
and deflection is pertinent, and his novel treatment of stresses 
in skin plating forms a valuable addition to the literature of 
the subject. 

As regards the method of determining bending moments 
and deflection of transverse girders given in the paper, it 
should have been there stated that the weight of the girder was 
disregarded in the desire to attain maximum stiffness. This 
concession on the part of the contractor was offset by a similar 
one on the part of the Bureau of Docks in allowing the use of 
the unit stress specified for self-docking operations for all cal¬ 
culations involving the assumption that the weight of the ship 
is carried on keel blocks alone. These provisions, together with 
others affecting methods of conducting tests, etc., were incor¬ 
porated in the contract as “Contractor’s Supplemental Specifi¬ 
cations." This will also explain the fact that in the paper only 
the calculated deflection for ship on keel and bilge blocks was 
given. It should be stated, perhaps, that computations, to all 
intents and purposes identical with those suggested by Mr. 
Laws, were made, and as the net result of allowing for the 
weight of the pontoon and side walls is the reduction of the 
end upward forces by an amount equal to the weight of the 
sides, both the bending and deflection under ship loads are re¬ 
duced. Inasmuch as experience with the Algiers dock led to 
some doubts of the practical value of theoretical methods of 
determining deflections, owing to the extraordinary effects of 


262 


FLOATING DRYDOCKS 


temperature changes, it was thought best to err on the side of 
safety and make for increased stiffness. 

Mr. Laws’ method of determining the thickness of the skin 
plating is ingenious, and his assumptions appear to be reason¬ 
able, yet, as the results obtained by its use are even greater 
than those obtained by the fixed-beam formula with span meas¬ 
ured from edge to edge of frame flanges, it would seem that 
efforts to reconcile formulas based upon the theory of beams 
with current ship practice are far from being crowned with suc¬ 
cess. In order to illustrate the difference which exists in the 
methods for determining the thickness of plates under water 
pressure, Table 5 is made up from ships actually in service or 
under construction, and represents the best shipbuilding prac¬ 
tice of the day. The age and service of the majority of these 
ships would seem to be a fair guaranty of safety. 

The results shown in Table 5 would indicate that the stresses 
in at least one instance equal the elastic limit of the materials, 
a condition of affairs which not only does not obtain, but 
which, in all probability, is not even approached. 

Mr. Laws’ criticism of the use of the term “critical points” 
in connection with the stability of the dock with ship is de¬ 
served. It was not the intention to convey the idea that at 
any normal position of the dock, either with or without ship, 
its stability is, in the ordinary sense, “critical.” but that the 
stability is least at or between the points indicated. 

The writer agrees with Mr. Le Conte in the opinion that 
there should be adequate berthing and docking facilities at 
every accessible port, and there is little doubt that, with harbor 
fees reduced or remitted entirely, the effect of such facilities 
would soon be felt, not only locally, but nationally. 

Mr. Le Conte’s recommendation as to the dimensions of new 
docks appears to be extreme. For commercial purposes, grav¬ 
ing docks of this size would require expensive pumping on ac¬ 
count of the small number of maximum-size ships which would 
be docked. The depth of 40 feet on the sill at high water would 
be an advantage, but it is doubtful if, at the present time, the 
additional expense is warranted. For naval purposes, this 


FLOATING DRYDOCKS. 


263 


depth is certainly desirable, but the length should be cut down 
to about 650 feet and improvement should be made in obtain¬ 
ing additional width of entrance. 

The writer agrees so nearly with Mr. Box that he finds it dif¬ 
ficult to reply to his discussion. The omission o,f the off-shore 
dock as an important, if not the most important, type of dock 
for commercial purposes, is a defect in the paper. This dock, 
on account of its economy and rapidity of operation, has held 
a high place in the esteem of the dock owners abroad, and will 
undoubtedly grow in favor in America. 

The comparison of quantities of water pumped from graving 
and floating docks drawn by Mr. Box is interesting in that his 
operations cover a large number of actual dockings, and neces¬ 
sarily include vessels varying in size. 

The building basin was originally constructed for the Algiers 
dock, which was completed in 1902. This was followed by 
the Dewey, begun in July, 1903, and launched in June, 1905. 
Since the completion of the Dezvey the basin has been out of 
commission, but it is understood that its use is contemplated 
for the construction of barges or other light-draught craft. 

Table 5. 


Vessel. 

Head at maxi¬ 
mum draught. 

Displacement : 
maximum 
draught. 


ft. ins. tons. 

Dock Dewey . 

35 0 

Ship A . 

22 9 13,000 

B . 

20 3 13,165 

c . 

22 8 12,500 

D . 

25 7 12,965 

E . 

26 3 11,650 

F . . 

26 11,700 

G . 

18 2 14,680 

H . 

26 9 15.9 00 

/. 

26 9 17,900 

J . 

15 2* 5 » 7 oo 

* 

>0 

II 

O 

b 

0 

0 

** 

to 

N 

II 

o 

1 

3 in.). 


Greatest unsup¬ 
ported rectangle 
a X b = sq. ins. 

Avg. thickness 
of skin plating 
at rectangle. 

Unit stress 

formula.* 

Unit stress.! 


ins . 

tons. 

tons. 

96 X 24 = 2,304 

19 
"52 

44 

5-33 

132X48 = 6,336 

1 9 

WJ 

13.07 

13.00 

102 X 42 = 4,284 

1 9 

3 2 

8-5 

8.54 

204X42 = 8,568 

1 

13-54 

12.74 

90X48 = 4,320 

1 

13.26 

11.63 

84X48 = 4,032 

f 

13.61 

H -55 

108 X 48 = 5,184 

t 

* 3-54 

12.74 

168 X 48 = 8,064 

1 9 

¥2 

10.43 

10.86 

72X48 = 3.456 


13-87 

10.81 

69X48=3,3*2 

1 

13-87 

10.52 

192X36 = 6,912 

i 

6.62 

7-85 


f Bach's formula for rectangular plates. 































266 


FLOATING DRYDOCKS. 


MODERN FLOATING DRYDOCKS.* 

By Civil Engineer A. C. Cunningham, U. S. N. 


General perfection in floating drydocks was reached with the 
type first and still known as the “balance dock,” which is also 
called the “solid dock” since the introduction of sectional and 
self-docking docks. The sketches in Diagram i show a plan, 





Diagram 1 .—The Solid Dock. 

end, and side elevation of a balance, or solid, dock. In pumping 
up one of these docks, the trim may be maintained by regulat¬ 
ing the amount of water retained in the side walls, which gives 
the name “balance dock.” 

These docks were originally and are still constructed in wood, 
and the inner faces of the side walls are generally given a batter 
to secure greater transverse stiffness of construction. In wood 
construction the dimensions and capacity of a solid dock are 
comparatively small on account of the weakness of the connec- 

* A lecture delivered before the class of Naval Architects at the Massachusetts Institute 
of Technology in March, 1906 . 

Reprinted by permission from “ Technology Quarterly,” Yol. XIX, No. 4 , December, 
1906 . 



















































FLOATING DRYDOCKS. 


267 


lions and limited strength which naturally accompany the ma¬ 
terial. 

The general cross section of the balance dock has prevailed 
through all subsequent forms of floating docks of recognized 
merit, and the more closely a modern floating dock approxi¬ 
mates to the original balance type the greater its value. 

When a solid floating dock reaches dimensions which pre¬ 
vent its entrance into a land dock for repairs, its life becomes 
limited. In wooden docks this life is of sufficient extent to 
return a profit on the investment, but it would not be with a 
steel dock. 

The solid dock was closely followed by the sectional dock, 
which is simply a series of small solid docks loosely connected 
together merely to preserve the alignment. The advantages 
of the sectional dock are that one section can be repaired upon 
another and, in wood construction, a much longer dock can be 
made operative than would be possible with a solid dock of the 
same material; an incidental advantage is that the sections may 
be divided into groups. 


Diagram 2.— A Sectional Dock. 

In Diagram 2 is shown a side elevation of a sectional dock o,f 
six sections which can be subdivided into various groups for 
independent use at the same time, and also a sketch showing 
one section turned 90° and docked on another. The disad¬ 
vantages of a sectional dock are the great care necessary to pre¬ 
serve the alignment and the difficulty of so adjusting the lift¬ 
ing force of each section that the docked vessel shall not be 
unduly strained or injured. No solid or sectional docks of any 
extensive magnitude have been constructed of wood. 





































































268 


FLOATING DRYDOCKS. 


Diagram 3 shows a modified form of sectional dock in steel 
construction. Figure 1 is a side elevation of the dock in align¬ 
ment ready for operation. Figure 2 shows one section docked 
on the others. A notable dock of this construction is that of 
Blohm and Voss, in Germany, which has a lifting capacity of 
17,500 tons. 

From the elevations it will be seen that this sectional dock in 
steel lacks continuity, and that the self-docking of the sections is 
a rather precarious proceeding. 

The construction of floating docks of any great magnitude in 
iron or steel requires that it should be possible to have access 
to the underwater portions for preservation and repairs. This 
led to the development of the general type known as self-dock¬ 
ing floating drydocks. As the modern ship of the first class, 
•and especially the warship, is a flexible and tender structure as 
compared with its short, broad predecessor in wood, it was 
necessary that these self-docking docks should have the greatest 
possible continuity and longitudinal stiffness. The sectional 
dock, pure and simple, has, in consequence, been eliminated 
from the problem, and an approximation to the solid or bal¬ 
ance dock is always sought. 




Diagram 3. —A Sectional Dock of Steel Construction. 


The first self-docking dock of any note that is still of im¬ 
portance is known as the Rennie dock, after Mr. George B. 
Rennie, the celebrated English engineer. 







































































FLOATING DRYDOCKS. 


269 


The Rennie dock is illustrated on Diagram 4. Figure 1 is a 
plan showing a pontoon being withdrawn preparatory to self¬ 
docking. Figuie 2 is a sectional side elevation showing a pon¬ 
toon self-docked. Figure 3 is an end elevation showing a pon¬ 
toon self-docked. 

This dock is a compromise, having the side walls of a solid 
dock and the pontoons of a sectional dock. For very great lon¬ 
gitudinal stiffness the side walls must be unusually high and 
wide, as any extensive or strong connections between the pon¬ 
toons are impracticable. The dock has the advantage of being 
easily const 1 ucted; the pontoons can be built and launched sep¬ 
arately, assembled after they are afloat, and the side walls 
then erected on them in place. The self-docking is simple in 
principle and requires no technical skill or instruction. 

The pumping of a floating dock is accomplished with cen¬ 
trifugal pumps, which should be placed as low down in the 
structure as possible, in order that they may not lose their 
priming in the last stages of pumping. These pumps dis- 
• charge directly outboard at their own level. As regards 
pumping plant, the Rennie dock is at a disadvantage. For 
economical construction the pumps must be placed in the side 




; 1- »-- n - 

■ n 







■ 

L ■ »l-- 

i' • 








Diagram 4 . —The Rennie Dock. 















































































7 


Diagram 5 .— The Ceark Dock 






























































































































































FLOATING DRYDOCKS. 


2-JI 

walls above the pontoons, and therefore have a long- suction 
in the last stages of pumping, which, if necessarily stopped, 

may lead to a loss of priming which may be difficult to re¬ 
store. 

A numbei of important docks have- been built on this prin¬ 
ciple; others are under construction and design in Europe, 
and the type will always be of importance on account of the 
ease and simplicity of construction. 

The next dock requiring consideration is the Clark type, 
designed bv Mr. Lyonel E. Clark, of the firm of Clark & 
Standfield, of London. The members of this firm are both 
descendants of a line of celebrated floating-dock designers 
and builders, and have done more towards advancing the 
interests and value of floating docks than any other indi¬ 
viduals in the world. 

The Clark dock is a modification of the Rennie dock, and 
is illustrated in Diagram 5. Figure 1 is an end view, in which 
it will be seen that the pontoons are placed between the side 
walls instead of under them. Figure 2 is a side view showing 
the manner of stepping back the side walls and the gang¬ 
way openings to which Mr. Clark has so far generally given 
preference, figure 3 is a plan showing the pointed-end pon¬ 
toons preferred by Mr. Clark. Figure 4 is an end view 
showing the end pontoons self-docked. Figure 5 is a sectional 
side view showing the central pontoon self-docked. Figure 
6 shows the manner of getting at the bottom of side walls. 
Figure 7 is a detailed elevation, and Figure 8 a detailed plan 
of the numerous taper-bolted tee and fish-plate connections 
between the pontoons and side walls. 

In this dock Mr. Clark has sacrificed the simplicity of con¬ 
struction and ease of self-docking of the Rennie dock to se¬ 
curing greater longitudinal strength and stiffness with prac¬ 
tically the same material. 

It is apparent that for Clark & Rennie docks of the same 
general dimensions the increased depth of side wall in the 
Clark dock gives much greater longitudinal stiffness. In the 
earlier Clark docks five pontoons were used, so that there was 


272 


FLOATING DRYDOCKS. 



'-N 




6 



not much gain in continuity of floor over the Rennie dock; 
but in later designs Mr. Clark has reduced the pontoons to 
the least possible number—three—so that with the long 
central pontoon the Clark dock has a much stiffer and more 
nearly continuous floor than the Rennie dock. In the pumping 
plant Mr. Clark also has the advantage of having the pumps 
located well down near the bottom of the structure. In locat¬ 
ing the pontoons between the side walls the lower connec¬ 
tions have been placed in a position where they are normally 
under water and inconveniently located for inspection and 











































































































































































FLOATING DRYDOCKS. 


2 73 


piesei vation. To bring the upper connections to a suitable 
height, altars must be added to the pontoons, which decrease 
the floor space and complicate the construction. 

The self-docking of a Clark dock requires skill and technical 
knowledge. The connections being all in vertical shear, the 
various combinations of side walls and pontoons used in self¬ 
docking must all be brought to the same flotation and buoy¬ 
ancy before the connections can be opened. The accumula¬ 
tions of mud in the pontoons and marine growth on the out¬ 
side constantly vary the flotations of the separate parts, and 
the cantings of the dock for partial and progressive open¬ 
ings of connections make it desirable that the self-docking 
should be under technical supervision. 

Another type of dock designed by Messrs. Clark & Stand- 
field is called the “one-sided” or “off-shore” dock. The dock 
may be attached to a floating outrigger or to a framework on 
the fore shore by booms having a parallel-ruler motion. It is 
generally made in two sections. The dock is illustrated in 
Diagram 6. Figure i is an end view of the dock attached to a 
f 1 amework on the fore shore. Figure 2 is an end view of the 
dock attached to an outrigger. Figure 3 is an end view of a 
proposed double dock of this type with floating outrigger 
between. Figure 4 shows the simple method of self-docking. 
Figure 5 is an end view of a modification of this dock, called 
a depositing” dock, with which a ship is lifted and placed 
upon a grid. Figure 6 is a plan of the depositing dock. The 
one-sided dock is well suited to ships having considerable 
inherent stiffness and no greatly concentrated weights. It 
is very convenient in narrow streams, as the ship can be taken 
on sideways. No shoring is possible on the off side, and in 
pumping up, care must be exercised to prevent a side launch 
or rolling over. 

These one-sided docks can not safely be used without their 
shore attachment or outrigger, as the omission of one side 
wall destroys the “balance” property. As soon as the pontoons 
are submerged, the shore attachment must be depended upon 
to preserve the trim, as slight variations in buoyancy are not 
t8 


274 


FLOATING DRYDOCKS, 






1- 


< 1 

' 1 

1 1 

1 1 

• ' 

1 ' 

1 • 

1 ' 




tr.. 


4 



Diagram 7. —Bolted Sectional Dock at Pola. 




































































































































FLOATING DRYDOCKS. 


275 


resisted and controlled as in the case of a two-sided dock. 
I 01 the same leasons the pumping - must be done uniformly 

and with care, in order not to cause a dangerous strain in the 
shore connections. 


The latest design of self-docking* dock made by Mr. Clark is a 
bolted sectional type for the Austrian Naval Station at Pola. 
This dock is illustrated in Diagram 7. Figure 1 is a side 
eleuation. Figure 2 is a plan. Figure 3 is a sectional side 
elevation of an end section self-docked. Figure 4 is a plan 




2 






Diagram 8. —The Cunningham Sectional Dock. 






















































































































































276 


FLOATING DRYDOCKS. 


of the central section self-docked. Figure 5 is a detail sec¬ 
tion of the chamber between sections which extends continu¬ 
ously around the sides and bottom. 

The location and extent of the connections between the sec¬ 
tions of the dock make it practically continuous and the near¬ 
est approximation to a solid dock that has yet been devised. 
This dock has not yet been self-docked, so far as can be ascer¬ 
tained, and considerable doubt exists as to the possibility of 
making or keeping the chambers between the sections dry, 
so that the connections will be accessible.* 

The self-docking of this dock is very similar to that of the 
modified sectional dock first described, except that, owing to 
the necessarily pointed ends of the end sections, less stability 
is secured. 

The self-docking docks so far described are all of foreign 
design and represent the progress so far made in the matter 
in Europe. 

Since the revival of general interest in floating docks in the 
United States further progress in the matter has been made in 
this country. The progress is based upon experience with 
the Clark dock and study of all existing and proposed types. 

On Diagram 8 is shown a modified bolted sectional dock 
proposed by myself about three years ago. Figure 1 is a side 
elevation of a dock begun with three sections and later ex¬ 
tended to five (two new ones dotted). Figure 2 is a side view 
showing the method of self-docking. Figures 3 and 4 are 
details showing different manners of connecting the sections. 
Figure 5 is an end view showing the lines and extent of con¬ 
nections. Figure 6 is a detail showing the connection of the 
pumping main between sections. In this type each section is 
a complete and independent dock in itself, and all sections are 
alike. The dock has the same advantage as the Rennie dock 
in that the pontoons can be built and launched separately, the 
side walls erected on them after they are afloat, and the sec¬ 
tions finally assembled and connected. When connected up 

* Since the writing: of this paper it has been learned that there is a land dock at Tola 
which will take the sections of this floating: dock, and there is no intention of self-docking: 
this particular dock: but the Trinidad Dock, a 4,000-ton dock, of the same design has 
recently been successfully self docked at the builders' yard. 




Plate 2.— U. S. Floating Dock “Dewey,” with Central Pontoon Self-Docked on the End Pontoons. 




















FLOATING DRYDOCKS. 


2 77 


the entire dock can be operated from the pumping plant on 
one section. The possibilities of extension or separation into 
groups with this dock are of considerable importance com¬ 
mercially. The self-docking is simple and requires no special 
instruction or technical knowledge. 

A disadvantage of the dock is that the pumping must be 
regulated from as many stations as there are sections. The 
repetition of sections does not give as great economy in dis¬ 
position and location of material as is possible in a solid 
dock, but this is larg'ely offset by the duplication of parts and 
labor, which simplifies and hastens the construction. 

The last floating-dock design that has been produced is that 
of the Maryland Steel Company, by Mr. Henrik Hansson, 
one of the assistant engineers. This design was produced to 
meet the rigid and extensive requirements of the Bureau of 
Yards and Docks’ specification for the Government dock in the 
Philippines, the most exacting specification for floating docks 
that has so far been issued. The design was accepted and the 
dock built by the Maryland Steel Company. 

The dock is illustrated on Diagram 9. Figure 1 is a side 
elevation. Figure 2 is an end elevation. Figure 3 is a plan. 
Figure 4 is a side elevation of the middle section self-docked. 
Figure 5 is an end elevation of the middle section self-docked. 
Figure 6 is a plan of the end sections self-docked. Figure 7 
is an end elevation of an end section self-docked. 

In the Maryland Steel Company dock great continuity has 
been secured. The side walls are continuous, and the long 
central pontoon is built solidly into them. The only break 
is in the short end pontoons, which form about one-fifth of 
the floor at each end, and the connections of these to the side 
walls and main pontoon are extensive and rigid. The low 
side walls on the end pontoons come into action only in self- 
dodcing, being ordinarily allowed to fill with water, and are 
again emptied automatically as the dock sinks and rises. These 
low side walls contain a pumping plant of sufficient capacity 
to operate the end pontoon, which is supplied with steam from 
a main boiler bv a flexible connection. Ordinarily the small 


278 


FLOATING DRYDOCKS. 


pumping plant in the low side wall is inoperative, the piping 
system of the end pontoon being connected to the main drain¬ 
age system by a joint like that previously shown with the 
Cunningham dock. 

In operation this dock has proved very rigid and reliable 
and easily operated. The self-docking has proven to be the 
easiest, simplest and most quickly accomplished of any yet 
tried. 

After this dock passes a certain length the width must also 
be increased in order to allow the end pontoons to be docked 
on the main portion. 

In designing a floating drydock the first matters receiving 
consideration are the clear width between the side walls, the 
draught over keel blocks, and the length. For a commercial 
dock the maximum ship entering the port does not receive 
consideration, but rather a ship somewhat above the average, 
as it is the average ship that brings the largest and most 
profitable business to the dock. Ships below the average are, 
of course, readily handled by the dock, but the nearer it is 
worked up to its full capacity the greater will be the profit 
in the investment. 

The determination of what will be the average ship during 
the life of the dock is a matter which requires careful consid¬ 
eration and study. Ships prefer to visit ports where there are 
docking facilities, and a large dock may invite larger ships 
than before cared to come. In any event, a large dock gives 
a port a favorable name among shipping interests. The com¬ 
ing growth in the size of ships in the future can not always 
be predicted by the past, and as a general rule it may be said 
that it is more often the case that docks are designed too small 
rather than too large. 

With military docks the case is somewhat different. Both 
the heaviest and longest vessels of a navy must be docked, and 
the heaviest and longest vessels likely to be built within a 
certain period are more easily predicted. At the same time 
liberal estimates should be the rule, for one warship that can 
not be docked at home may place a navy in a serious predica¬ 
ment. 


FLOATING DRYDOCKS 


279 









Diagram 9.—The “Dewey.” 















































































































































































28 o 


FLOATING DRYDOCKS. 


The clear width between side walls of a floating dock is not 
difficult to decide upon. It so happens that structural reasons 
have limited the maximum width of entrances to land dry- 
docks throughout the world to 80 feet, and so by taking this 
dimension any ship now existing can be got into a floating dock, 
and for the average widths there will be a fair clearance for 
working space. This width is also desirable for general lateral 
stability of the dock. In the case of the United States govern¬ 
ment floating drydocks, the standard clear width between side 
walls is ioo feet. It is interesting to note that the maximum 
width of drydock entrances throughout the world is one of 
the limiting factors of ship development. 

The draught of water over the keel blocks must, of course, 
accommodate the normal draught of the maximum ship for 
which the dock is designed. In addition to this, provision 
should also be made for abnormal draught due to accident, and 
as a rule it is a wise proceeding to provide for the greatest 
draught of ship that is likely to be able to enter the port 
during the life of the dock. In military docks a deep draught 
over the keel blocks is of especial importance, as these docks 
are more likely than others to be called upon to handle dis¬ 
abled ships at an abnormal draught. 

The length of a dock and its lifting capacity are two func¬ 
tions so closely related that they are best treated together, and 
the matter is most comprehensively considered in the case of a 
military dock. The military dock is called upon to deal with 
short battleships, long cruisers, and perhaps, in times of war, 
with still longer merchant ships that have been converted into 
naval auxiliaries. Full bearing length must be provided for 
the longest ship, and in addition a working platform is desi¬ 
rable under the ends of the ship that do not require bearing. 
This bearing length and working platform consist of the pon¬ 
toons of the dock which give the lifting power, and' there is 
a natural desire to utilize, so far as may be safely done, their 
entire displacement for lifting purposes. 

The conditions to be met in the question of the length 
and lifting power of a floating dock are illustrated on Diagram 



Plate 3. — U. S. Floating Dock “Dewey,” with End Pontoons Self-Docked on the Central Pontoon. 


























































































.* 













FLOATING DRYDOCKS. 


28 l 






10, in which it is to be understood that the figures are dia¬ 
grammatic only and for the purpose of illustration. In Fig¬ 
ures 1 and 2 the docks are identical and the ships of the same 
weight, but of different bearing lengths. The dock has been 
designed just to lift the longer ship with all pontoons pumped 
empty. The bending strains for which the dock is designed 
under these conditions are the ordinates of the curve. Now 
to lift the short ship the pontoons must again all be pumped 
empty, but the upward leverage of the pontoons which are 



















































































































































































































282 


FLOATING DRYDOCKS. 


unopposed by the ship will greatly increase the bending stress 
and cause the curve to rise, perhaps to a point indicating dan¬ 
ger or failure of material. The bending strains may be re¬ 
duced by leaving water in the end pontoons, as in Figure 3, 
but under the conditions assumed the ship will not then come 
entirely out of the water. If the docks in Figures 1 and 2 
are to have the same lifting capacity and are to lift both the 
long and short ships, there remains but one thing to do, and 
that is to increase the girder strength by raising the side walls, 
as shown by the dotted lines in Figure 3. In actual prac¬ 
tice a compromise will give the best results, the side walls be¬ 
ing raised somewhat to increase the girder strength and the 
pontoons deepened to give some excess of lifting capacity. 
In this compromise the condition of pumping and flotation are 
shown in Figures 4 and 5, and the bending strains are prac¬ 
tically the same in both cases. This compromise necessitates 
skilful and intelligent pumping with short, heavy ships until 
the weight of the ship becomes less than the lifting capacity 
of the pontoons directly under it, after which pumping may 
proceed uniformly all over the dock without danger. 

The United States government has been the first to refuse 
this compromise in the military dock for the Philippines, pre¬ 
viously described. In that dock uniform pumping without 
undue strain is required for any load that it is possible for the 
dock to take. This would not be an economical requirement 
for a commercial dock, but in a military dock it insures many 
desirable qualities. It permits the most rapid lifting under all 
possible conditions. It is a safeguard against all careless and 
ignorant pumping which might be possible in emergency con¬ 
ditions. It makes it possible to hog or sag a ship on the dock 
for special repairs. It makes it possible to dock a ship near the 
end of the dock and also to dock it on an incline. 

The general stability of a floating dock varies directly as 
the square of the number of watertight divisions. This is 
illustrated in Diagram 11. Figures 1 and 2 are cross sections 
of pontoons, having two and four watertight compartments, 
respectively. The comparative stability of these as affected by 


FLOATING DRYDOCKS. 


283 


the shifting of water ballast due to heeling is four to sixteen. 
The desirable longitudinal girders in a floating drydock, shown 
in Figuie 3, make six lateral compartments possible in con¬ 
nection with the structural design, so that in practice the shift¬ 
ing of water ballast from heeling is quite small. 

d he stability of a dock under various conditions in lifting 
a ship and in self-docking its own parts is an important matter. 
In the lifting of a ship the case is shown in Diagram 11, Figure 


1 2 



STABILITY = 4- STABILITY - 16 



W-W = WATER PLANE 

G= CENTER OF GRAVITY OF COMBINATION 
C-L = LINE OF GRAVITY 

8 = CENTER OF BUOYANCY OF COMBINATION 



B * M 1 LINE AND DIRECTION OF BUOYANCY 
M = METACENTRE 

G - M = METACENTRIC HEIGHT OF COMBINATION 
G "X = RIGHTING LEVER 


Diagram 11 .—Correlation between Stability and Number of 

Water-tight Divisions. 


4. In this figure it is apparent, and it is confirmed by calcu¬ 
lation, that the stability is the least with the water plane be¬ 
tween the bottom of the ship’s keel and the deck of the pon¬ 
toons, for in this position the ship’s buoyancy has entirely left 
the combination, the buoyancy of the pontoons themselves has 
not yet come into play, and the comparatively slight buoyancy 
of the side walls is all there is to resist overturning. The 
stability of the combined ship and dock at this particular period 
may be largely controlled by the pumping in a dock where but 
little shifting of water ballast is possible, for the more nearly 
the dock is kept level the greater the metacentric height. With 
























































284 


FLOATING DRYDOCKS. 


a well-designed floating dock it is an easy matter so to conduct 
the pumping that the dock will never be more than from 6 
inches to 1 foot out of level, and under no circumstances is it 
necessary that the dock should be more than 2 feet out of 
level in raising a ship. Two feet out of level, however, is only 
about 1 degree with a fair-sized dock, and may be taken for 
the possible list in considering stability. Using 1 degree as 
the possible list of the dock after the ship is entirely out of the 
water and before the pontoon decks have come above the sur¬ 
face of the water in sufficiently numerous calculations has 
shown that the metacentric height for this position of least 
stability will vary from 5 feet to 20 feet, according to the 
cross section of the combination of ship and dock. In com¬ 
parison with the metacentric height of a ship that may be 
from 1 to 3 feet with the same degree of heel, the great 
stability of a floating dock under the worst condition is at once 
apparent. The stability of a floating dock of approximately 
standard cross section and design is so well assured that the 
calculations are more a matter of interest than necessity. 

Apparently the most unstable position of self-docking shown 
in the preceding diagrams is that of the main portion of the 
Maryland Steel Company dock; but even in this at the plane 
of least stability the metacentric height is 17.82 feet. 

The next matter for consideration is the deflection of a 
floating drydock under the various loads and conditions. The 
longitudinal deflection under the maximum loads is a matter 
which gives more concern to designers than any other con¬ 
sideration. It is the governing factor in the relation of length 
to total lifting power, height of side walls, and total amount 
of material entering into the structure. The earlier floating 
docks had to deal with comparatively short ships of consid¬ 
erable inherent stiffness, but the modern floating dock, and 
especially the military dock, has to deal with ships both long 
and short, having great weight unevenly distributed and con¬ 
siderable flexibility when not water borne. Some designers 
have prided themselves on the small weight of their docks 
compared to the total lifting power, frequently getting the 


FLOATING DRYDOCKS. 


285 


structural weight of the dock less than 40 per cent, of its 
total displacement capacity. Such docks will always give a 
large deflection, and as they deteriorate from age may be¬ 
come a menace to themselves and the ship they carry when 
worked up to their apparent capacity. 

Under the possible load which a dock can lift, which is de¬ 
termined by its displacement, there is certain to be deflection, 
as the dock is built of elastic material and supported by a liquid 
medium. This greatest possible deflection should be confined 
within safe limits, both for the ship and dock. 

Having determined and limited the greatest possible de¬ 
flection, the deflections of the dock at its rated capacity must 
be established. 

Until recent years dock designers have been largely satis¬ 
fied with safely lifting a ship and returning it to the water 
uninjured, and as long as this was the ruling condition there 
could be no marked advance in floating docks. 

The United States Government, in its new floating dock 
for the Philippines, has inaugurated a new deflection require¬ 
ment that marks a decided and important advance in this 
line. 

The deflection of the dock is limited to a small amount under 
the full rated capacity, with the dock pumped uniformly all 
over. 

The full effect of limited deflection under uniform pumping 
is best shown by a comparison. In the Government dock at 
New Orleans uniform pumping was not specified; the dock is 
525 feet long, has a rated capacity of 15,000 tons, a displace¬ 
ment of 18,000 tons, and a total weight of about 6,000 tons. 
The new Philippine dock, in which uniform pumping was 
specified, is 500 feet long, has a rated capacity of 16,000 
tons, a displacement of 22,000 tons, and a total weight of 
about 11,000 tons; when pumped in the manner allowed for 
the New Orleans dock it will dock a 20,000-ton battleship with 
only slight deflection. ' (Limiting the deflection under uniform 
pumping has, therefore, about doubled the strength of the 
Philippine dock as compared with the New Orleans dock.) 


t 


286 FLOATING DRYDOCKS. 

Some of the reasons for uniform pumping in a military clock 
have already been given. Other reasons are that a clock so 
designed can be water ballasted until the deflection under the 
rated load is all removed and the ship brought to a straight 
keel or even hogged. Repairs and changes can then be made 
under the same conditions as when a ship was built, the struc¬ 
tural advantages of which are great. 

This liberality of design which is desirable in a military 
dock may not always be expedient in a commercial dock, but in 
any event the deflection should be kept within the safe limits 
of the elasticity of any hull which it is possible for the clock 
to lift. 

On account of the shorter span and the necessary uniform 
pumping, athwartship, the transverse deflections in a dock are 
more easily dealt with, but they should always be calculated 
and limited without estimating on the use of shores from the 
side walls of the dock to the ship. 

The dimensions arid capacity of a floating drydock having 
been determined and its structural strength decided, there re¬ 
mains to be selected the method of self-docking that will best 
suit these conditions. 

The preservation of a large floating drydock is of so much 
importance that there is sometimes a tendency to give the 
self-docking feature an ascendency over the regular functions 
and purposes of the dock. 

In general, the following principles should govern the self¬ 
docking features of a floating drvdock: Great continuity in 
docking operations; smallest possible number of divisions and 
auxiliaries; joints at greatest possible distances from points 
of greatest strain; joints always dry and accessible; simple 
and easily understood method; remoteness or impossibility of 
accident in self-docking; largest possible stability and strength 
when self-docked; quickness of self-docking and reassembling. 

Many of these desirable features are antagonistic, and how 
well they have been met, co-ordinated and reconciled up to the 
present time can be seen by a study and comparison of the 
types previously presented. These types, it is believed, repre- 






FLOATING DRYDOCKS. 


287 


sent the best of every class that has been devised, and under 

them there are many unimportant and mostly valueless varia- 
tions. 



Diagram 12.— Docks with Caisson. 

The quickness of self-docking is a most important matter in 
any dock, but especially so in a busy and prosperous commer¬ 
cial dock. If self-docking is long, complicated or liable to give 
trouble, it will never be attempted until absolutely necessary, 
and in the meantime the under-water portion of the dock struc¬ 
ture may have suffered much deterioration. 

The best record yet made in self-docking is that of the new 
government drydock for the Philippines, which was self- 
docked and reassembled on the first trial in fourteen days. It 
is believed that on a subsequent trial this time could be re¬ 
duced to ten days. 

This does not take into account any extensive cleaning or 
painting that might be desirable, and to completely clean and 
paint the submerged portions of an extensive floating dock 
would, under the most favorable conditions, require from one 
to three months. 

The more experience that is gained with self-docking docks 
the more desirable does a return to the original solid type ap¬ 
pear. To this end an adaptation of the ship caisson has been 
proposed in this country, and is understood to have been tried 
unsuccessfully in Europe. The application is-illustrated in Dia¬ 
gram 12. Figure 1 is an end view of a dock with a caisson ex¬ 
tending entirely across the bottom and up both sides above 
the water line. Figure 2 is an end view of a dock with a 
caisson extending just past the center and up one side. These 
caissons are entirely open on the sides next the dock. The 


































































288 


FLOATING DRYDOCKS. 



m 











_ 










i 



. 




Diagram 13. —The New Cunningham Caisson. 

B, pump; F, flushing valve; M, flotation chamber; N, packing ring; P, pump valves; 

IV, working chamber. 


proposition is to make them watertight against the dock, and 
then pump out the contained water, so that the submerged por¬ 
tions of the dock will become accessible. The difficulties to be 
encountered with these caissons are evident. In Figure i it 
would be a mechanical impossibility to make a watertight joint 

















































































































FLOATING DRYDOCKS. 


289 

on both sides at once, and the sag would leave more or less 
opening at the bottom. In Figure 2 there would be much 
difficulty m controlling the caisson, and the end under the dock 
could not be got up sufficiently tight against the dock to make 
pumping effective. I have recently proposed a caisson, which 
is here generally announced for the first time, which has worked 
satisfactoi ily in a scale model and which may possibly solve 
this problem. The caisson is illustrated in Diagram 13. Fig- 
me 1 is a plan of the caisson. Figure 2 is an end view of a 
dock with a caisson extending entirely across before lifting 
against the bottom. Figure 3 is an end view of a dock with 
a short caisson sealed against the bottom. Figure 5 is a 
sectional elevation, and Figure 6 a sectional plan of the cais¬ 
son, showing the general arrangement. 

The action of this caisson is as follows: Water is admitted 
to the main chamber freely until the combination is sunk as 
far as the displacement of the supplemental chamber will per¬ 
mit, which is less than submergence. Water is then carefully 
admitted to the supplemental chamber until the combination 
just loses its buoyancy. The caisson then sinks until arrested 
by the floats attached to the entrance shafts, and is then ready 
to move into position under the dock. In the case of the short 
caisson an approximate level is maintained by counter-balanc¬ 
ing the caisson chamber. Being in the desired position, the 
water is exhausted from the supplemental chamber and the 
caisson rises and seals against the bottom of the dock, after 
which the main chamber can be pumped dry, giving access to 
the bottom of the dock. The manner of gaining access to 
the edges of the dock is shown in Figure 4. The caisson is 
sealed against the bottom of the dock, with the end projecting; 
the edge of the dock and the projecting end of the caisson 
are then canted out of water, after which the main caisson 
chamber can be pumped dry. 

The successful application of the caisson to the bottom of a 
floating drydock will permit a return to the solid type to which 
all self-docking docks strive to approximate. It will further 
permit of the painting or repair of the bottom of the dock 
19 


290 


FLOATING DRYDOCKS. 






5 





- rh — 






' 

1 

1 

11 

1 1 



: 1 

11 

11 

— -- 11 

n 


li 

II 1 

1 

1 

, 1 


Diagram 14. —General Principles of Floating Drydock 

Construction. 




























































































































FLOATING DRYDOCKS. 


291 


at the same time that a ship is undergoing repairs in the dock; 
and the only time that the dock can not be in use is when 
woi king on the edges. In the solid dock the construction will 
not only be stiengthened and simplified, but the pumping sys¬ 
tem as yell will be much more simple and easily arranged. 

The general principles on which all floating drydocks are 
constructed aie illustrated in Diagram 14. Figure 1 is a plan 
view of the pontoon or body of the dock, with the lines of 
gilders. The solid lines are watertight bulkheads, and the 
dotted lines are open bulkheads, or trusses. Figure 2 is a 
plan view showing the watertight compartments alone and the 
piping leading into them from the pumping main in the side 
wall. There may be a pumping main in each side wall, but 
it is considered better practice to have it only on one side, as the 
pumping is then more directly under the observation and con¬ 
trol of the dockmaster. Each pipe is controlled by a quick- 
acting wedge valve. For the easier regulation of the pumping, 
the balancing of the dock, and the application of the lifting 
power in the correct manner the watertight compartments are 
collected into groups, as shown in Plan 3. The valves of all 
the pipes leading into a group are coupled to one valve rod, 
so that all are opened or shut together. All the valve rods 
are brought to one station by a system of bell-crank levers, 
and at this station the dock master regulates the entire pump¬ 
ing of the dock. Figure 4 is an end elevation of the dock, 
showing the longitudinal lines of watertight bulkheads. The 
pumping main, with pump located on top, and discharge out¬ 
board are shown, and also the flooding inlets and the lead 
of a pipe to a compartment. 

Figure 5 is a side elevation of the dock, showing the framing 
and bulkheads in the side walls, the engine deck with engines 
and boilers, and the pumping main with its pumps and flooding 
inlets. Three pumping units are the least that should be in¬ 
stalled on a large floating dock in order to secure a fairly uni¬ 
form flow of water from all compartments and to provide 
against serious disablement in case of any breakdown. (In 
the case of a commercial dock whose location is fixed, the 


292 


FLOATING DRYDOCKS. 


pumps may be operated to advantage by motors supplied with 
power from a station on shore.) 

In docking a ship the following method of pumping will 
always be correct, whether the dock is designed for uniform 
pumping or not. The ship having been centered, pump uni¬ 
formly until the ship is seated firmly, it making little dif¬ 
ference whether the blocks are taken at the bow or stern first; 
if there is any preference it is usually the bow. After the 
ship is seated pump from the center of the dock first, gradu¬ 
ally extending the pumping towards the ends in the order in- 



Diagram 15. —Method of Placing a Ship in Dock. 


dicated by the numbers in Figure 3, Diagram 14. The pump¬ 
ing of the side walls is held back to secure quick balancing, 
and incidentally for priming the pumps if the pumping is tem¬ 
porarily stopped towards the last stages. Only slight regula¬ 
tion of valves is necessary to keep the dock level where the 
arrangement of groups is correct and where there is an ample 
flow of water through the pipes. 

The side-wall decks of a dock should be fully equipped with 



































floating drydocks. 


293 


capstans, fairleads and bitts. A bridge at the forward end for 
a headline is desirable, but not absolutely necessary. With 
four moorings at the entrance of a dock, it is entirely possible 
to take a ship in without the use of tugs. On Diagram 15 is 
shown the placing of a ship in dock. Figure 1 is the ship held 
by the buoys and with a headline out. Figure 2 shows the 
ship about one-thud entered and the lead of the lines at that 
time. Figure 3 shows the ship three-quarters entered and the 
lead of the lines. Leaving the dock is easier than entering it, 
for as soon as the ship’s stern is clear she may be started astern 
and clear the dock very quickly. 



2 


Diagram 16.-- Arrangement of Blocking on a Government Dock. 

The Government requires that the pontoon decks of its 
docks shall be made sufficiently strong to take blocking at any 
point; so far this has not been generally the case with com¬ 
mercial docks, but it is a valuable property and deserving of 
consideration for all docks. The arrangement of blocking on 
a Government dock is shown on Diagram 16. Figure 1 is a 
plan and Figure 2 an end elevation. Shores may also be used 
from the stages on the side walls. 

The limited width of the entrances to land drydocks and its 
effect on the development of ships have been referred to. The 





















294 


FLOATING DRYDOCKS. 


depth of water over the sill of land drydocks is anothr limit¬ 
ing factor of ship development; and when it is considered that 
from five to eight years are required for the construction of a 
land drydock, it would seem as if any general increase in the 
size of ships had nearly reached the limit at the present time. 
Should any radical development in ship design be deter¬ 
mined on, the immediate relief will be found in the floating 
dock, for it can be constructed of any dimensions and capacity 
desired in less time than a ship can be built, and it can be 
towed to any location desired. 

The extent of this paper only permits of the treatment of 
the most general and important principles of floating drydocks. 
While the details are both important and interesting, a general 
and comprehensive understanding of the subject is the best 
foundation for those who desire to go farther into the ques¬ 
tion. - | | 1 








FLOATING DRYDOCKS. 


295 


THE MOVABLE BASE.* 

By Civil Engineer A. C. Cunningham, U. S. Navy. 


The popular conception of a modern navy is an aggregation 
of fighting vessels varying from the small torpedo boat to 
the great battle ship. The speed, armament and general 
efficiency of these vessels have the attention of the general pub¬ 
lic, and their personnel is a matter of keen interest and de¬ 
served pride, in our own country at all events. Beyond these 
points the general interest and information rapidly wane, 
which is but natural and to be expected. How a ship is built, 
equipped and kept efficient is so largely a matter of techni¬ 
calities that it is outside the interest of the public at large, 
and not the least reason for this lack of interest in technicali¬ 
ties, in the United States, at least, is that the history of our 
Navy from its beginning to the present time is a record of 
unbroken successes in the various emergencies through which 
it has passed. There have been times when its ships have 
become antiquated in type and reduced in numbers almost to 
obliteration, but the spirit, tenacity and ability of its personnel 
have never failed or lagged even under the greatest discour¬ 
agement. 

When comparisons are made of navies they are generally 
based on tonnage displacements, armaments and types of ves¬ 
sels without regard to the means of maintaining their efficiency 
and effectiveness at all times and under all conditions. 

The most efficient fighting ship is the one that is in the most 
perfect condition as to hull, machinery, armament and equip¬ 
ment; which has fuel bunkers full, a complete supply of am¬ 
munition, and whose officers and men are well trained and 

* Reprinted by permission from the Proceedings of the United States Na\ al In¬ 
stitute, Vol. XXX, No. 1, Whole No. 109. 




296 


FLOATING DRYDOCKS. 


disciplined and in the best of health and spirits. How long- 
can a ship remain in this perfect condition? The fuel supply 
begins to diminish from the time of putting to sea; if it is 
in time of peace the trip is so laid out that fuel can be re¬ 
newed at certain ports of supply, but in time of war this one 
question of fuel alone may greatly limit the radius of action. 
If at rest the bottom is becoming foul and deteriorating, and 
the ship is constantly becoming less capable of making speed 
at any time. The stress of a chase or the severity of an en¬ 
gagement may render repairs to machinery very necessary, or 
a fresh supply of ammunition imperative, even in the event 
of a ship not having suffered other injury or loss. The strain, 
both mental and physical, is much greater on officers and men 
in time of war, and without estimating on the possibilities of 
epidemics, it is likely that the personnel of a war vessel may 
need partial renewal more frequently during war than in 
peace. 

It is not necessarv to follow this line farther to show how 
dependent a navy is upon its dock yards and supply stations, 
not only for its efficiency but for its continued existence, and 
more especially in war than in peace. 

The policy of the United States has always been defen¬ 
sive, particularly of its own rights and broadly of sound prin¬ 
ciples. While it remained a continental country its dock yards 
and stations must necessarily be 011 the continent, and from 
them all naval defense would start. The acquirement of insu¬ 
lar possessions renders the continental dock yards and stations, 
alone, insufficient for naval defense, for no extensive opera¬ 
tion or supervision can be conducted without a convenient 
base of repair and supply. 

The extent of naval operations depends upon how long a 
ship may remain away from a base of supply and repair and 
still be efficient, or how far it may leave such base with rea¬ 
sonable chance of return. When active defense becomes 
necessary the regular bases of a navy may prove inconven¬ 
iently remote for its operation to the best advantage. It then 
becomes desirable to establish a base at or near the scene of 


v 


FLOATING DRYDOCKS. 


297 


operations, but this may be in hostile territory or in a country 
wheie a permanent base would be valueless when the emer¬ 
gency had passed; moreover, an efficient permanent base re¬ 
quires years in building, as its basis is the drydock, which is 
the. one thing which cannot be extemporized, and without 
which no ship can be maintained in perfect condition. 

In defensive naval warfare we cannot choose the points 
where we will be attacked, but we can safely predict that they 
will be where we aie the least defended, and where our ships 
are the most likely to be met in the least state of efficiency. 
Such points ai e matters of common knowledge to the world, 
and whether their attack result in the defeat of a fleet or the 
destruction of a city the result is equally disastrous. 

These conditions and possibilities suggest a movable base 
which can be taken to the scene of operations, and which 
should supply all of the essentials of a completely fitted base 
of the permanent type. Even the movable base does not supply 
all that is desirable for modern operations, for, as far as pos¬ 
sible, the greatest efficiency is secured when necessities are 
taken to the fighting ship and it is not compelled to go for 
them. To secure this last desirable condition, the movable 
base should consist of units each of which, where possible, 
should farther constitute a flying sub-base which can search 
employment when not operating directly with the movable 
base, or when more urgently needed elsewhere. 

FLOATING DRYDOCKS. 

The essential element of a movable or temporary base exists 
in the floating drydock, but until Spain sent such a dock to 
Havana, it may be said to have been a dormant military idea. 
That dock was intended for war ships, and the existing con¬ 
ditions at the time the dock was installed rendered the fact 
of unusual significance. The failure of the dock to pass its 
tests, and its various mishaps of accidental sinking and failure 
of machinery, partly through mismanagement and partly from 
too economical designing, tended to mask the true value of 
these structures, and obscured the importance of the maneuver 


298 


FLOATING DRYDOCKS. 


of towing the dock from England to Cuba. This unfortunate 
dock was finally broken almost completely in two while being 
self-docked, and had this accident happened before the United 
States had taken the initiative with this class of structures for 
war purposes, it is difficult to predict how many years might 
have elapsed before a complete movable base would have been 

m 

possible. 

The United States was the first country to provide itself 
with a thoroughly modern floating drydock suitable for mili¬ 
tary purposes, but was so closely followed by Great Britain 
with her new Bermuda floating dock that no great advance 
can be claimed in inaugurating a new possibility in naval war¬ 
fare. Neither was the full military possibility of the American 
dock generally recognized when it was provided, as it was in¬ 
tended for installation in the Mississippi River at New Or¬ 
leans where land drydocks had been considered practically im¬ 
possible of construction, and thus the primary cause of its 
existence was topographical and not strategic. 

The full significance of a military floating dock was first 
realized when the United States recently provided for such a 
structure for the Philippines. The New Orleans dock had 
just proved a successful experiment; it was of British design 
but built under a general specification of the Bureau of Yards 
and Docks, and while it performed much more than was re¬ 
quired, not the least important thing learned during its con¬ 
struction and testing was that more should be demanded of 
these structures than had hitherto been the case. At this time 
the establishment of a naval base in the Philippines was one 
of the most urgent problems confronting the nation: one de¬ 
manding the utmost care and not possible of quick execution, 
even were the solution readily apparent. The floating dock 
happily relieved the situation; the essential of a naval base 
was provided, and if one location did not prove satisfactory 
another could be found. Profiting by the experience gained 
with the New Orleans dock the requirements for the Philip¬ 
pine structure have been made more exacting and comprehen¬ 
sive than has ever been the case with any previous floating 


FLOATING DRYDOCKS. 


299 


dock m the world. The requirements demanded of it are so 
far in advance of those demanded of the New Orleans dock 
that its success is assured in advance. Structures of this class 
have been towed across the Atlantic Ocean and the North 
Sea and then seawoi thiness has been fully demonstrated, but 
the towing of the Philippine dock half way around the world 
\\ ill be the final demonstration of the mobility of these struc- 
tuies, and will be a naval maneuver of the greatest interest 
to all nations. 

Considered as the basis of a movable base, the possibilities 
of the floating drydock are yet far from being fully developed. 
By increasing the width of its side walls extensive shops may 
be installed on the dock itself and other desirable installations 
may be made, wdiile the increase in side w^all width also per¬ 
mits the installation of traveling cranes capable of handling 
the heaviest machinery and armament. 

Repairs and preservation of w r ar ships are too often con¬ 
sidered from a peace basis alone; from such a basis the land 
drydock has many attractions, but as a war tool the ad¬ 
vantage is with the floating dock. We are rapidly nearing 
the draught of ships which requires a depth for land drydocks 
that renders them enormously costly, very difficult and slow r 
of construction, more liable to failure from increased hydro¬ 
static pressure, and in which no excess of depth is provided 
for emergencies. In time of war we may expect to deal with 
ships that are badly listed, down by the head or stern, or at 
an abnormal draught from injuries, and it is in such cases that 
the floating dock show’s its superiority. It can readily be con¬ 
structed for any possible emergency draught at slight increase 
of cost, and can be listed and depressed by the head or stern 
to take in a wounded ship that it might be impossible to enter 
in any land dock that w r e have under construction or pro¬ 
jected. Sufficient depth of water is essential for the operation 
of a floating dock, and in maximum cases it must be from fifty 
to sixty feet and should be comparatively smooth, though a 
strong current is not objectionable. A ship once in the dock, 
however, it may be towed into a sheltered position which the 


300 


FLOATING DRYDOCKS. 


ship alone could never reach, as these docks only draw from 
sixteen to eighteen feet with their full load. 

In the development of the military floating dock it is en¬ 
tirely practicable to equip them with a hydraulic dredging 
apparatus with which they can make their required depth of 
water without seeking it, and by arranging the dock pumps 
to discharge under the bottom of the dock in suitable places, 
the dredged site can he constantly maintained, or even made 
without other aid, in a soft or sandy bottom. The hydraulic 
dredging apparatus installed on a floating dock may be of 
farther strategic value for improving the entrance to harbors, 
or even obstructing them, if advisable. 

As the basis of a movable base the floating drydock is the 
unit which will give the most anxiety when moved during time 
of war. Its progress in towing from point to point must be 
slow, and unless strongly convoyed it invites capture or de¬ 
struction by an enemy. This danger may be reduced to a 
minimum by using the dock composed of complete and inde¬ 
pendent sections which are strongly connected into one unit 
when in use, but which are separable into sections for self¬ 
docking and other purposes; when separated into sections 
each one may be towed by a different route and at a different 
time. If the number of sections is in excess of the maximum 
requirements, the loss or capture of one is not serious, and the 
gain to an enemy is practically nothing. In any event the 
towing of a drydock can be made an invitation to battle that, 
if accepted, might culminate a naval war. 

t 

REPAIR SHIPS. 

Another unit of the movable base is the repair ship. The 
equipment of the floating drydock as a repair shop in no way 
curtails the usefulness of the repair ship, but rather increases 
its radius* of useful action by leaving it free to attend to such 
ships as do not need actual docking. 

The repair ship should be as completely fitted out for a re¬ 
pair shop as it is possible to so do with a floating structure, 
and the equipment may readily be carried to shears, punches 


FLOATING DRYDOCKS. 


301 


and steam hammers. A varied assortment of repair material 
should be carried in abundance, and artisans should largely 
constitute the crew. 

The dut\ of the lepair ship is to put in order the vessel that 
does not actually need to be drydocked for relief, and the ma¬ 
jority of external and internal injuries above the water line 
may be made good by this ship. When the temporary base 
has been established the lepair ship goes from vessel to vessel 
needing its services, transferring artisans and materials for 
such repairs as can be made on board the injured ship itself, 
and in the meantime fabricating such material as requires its 
more extensive equipment and preparing it for transfer and 
installation at such time as it becomes ready. 

These are the duties of the repair ship as a unit of the mov¬ 
able base, but it should still farther constitute a flying sub¬ 
base capable of searching a cruising ground for vessels in need 
of its services, and to this end should have speed equal to any 
vessel of the fleet. Such speed not only insures prompt ser¬ 
vice in time of need, but enables the repair ship to accompany 
a fleet without decreasing the efficiency, and permits it to 
cruise in time of war with the least danger of capture. 

If a vessel is found by the repair ship to be in too serious 
a condition to be promptly and effectively benefited by its ser¬ 
vices, it may serve to tow the disabled vessel to the floating 
dry dock where repairs can be made to better advantage, and 
the repair ship thus left free to carry its services where they 
will be of greater advantage. 

COLLIERS. 

No matter how formidable or efficient a fighting ship may 
be it must have fuel in abundance for the best results, and if 
a certain and ample supply is always sure, its possible radius 
of action is unlimited. Without fuel, defense is not only 
weakened, but attack is impossible. Stationary coaling stations 
<lo not insure a constant and unlimited supply of fuel, nor do 
ordinary colliers in time of war. The ordinary collier may 
form an important unit of the movable base for the supply of 
such ships as may visit it, and may well be employed in coal- 


302 


FLOATING DRYDOCKS. 


in g ships which are in the floating clock or are receiving* the 
attention of the repair ship, but considered as sub-bases they 
fail in efficiency. As a sub-base the collier should have speed 
equal to the fleet, that it may not retard the same, may quickly 
join it, or may evade pursuit and capture, and its fuel-carrying 
capacity should be very great. Having these qualities it is 
still essential that the collier should be able to transfer fuel 
in any condition of sea or weather, to become in anv manner 
an ideal adjunct to a fleet. 

The transference of coal at sea is as yet an imperfectly 
solved problem. Sufficient experiments have been made to 
demonstrate that coal can be transferred from a collier to a 
war ship at sea when the latter is towing the collier, and a 
trolley system has been rigged between the masts of the two 
vessels. The transference, however, becomes more slow and 
difficult as conditions of sea and weather become worse, and 
as considerable speed of towing is necessary and much sea 
room required, conditions will be reached when more coal is 
burned in the operation than will be transferred, or a ship will 
be obliged to abandon an important strategic position which 
may never be regained. A collier of the capacity desirable for 
extensive and distant operations could not well be towed by 
a moderate sized war ship, nor a collier without masts be used 
with this method, so that its usefulness and possibilities are 
limited. 

It is desirable that coal should be transferred at sea at any 
time and in any condition of sea or weather as rapidly as pos¬ 
sible. 

It has recently been proposed to transfer coal at sea with 
the war ship and collier alongside of each other and prevented 
from colliding by forcing strong jets of water towards each 
other from different points below the water line. The pro¬ 
posal is attractive, and, if its expectations are realized, much 
more than the transference of coal at sea will be solved. Fitted 
with such an appliance the repair ship would be enabled to 
operate alongside other ships under conditions otherwise im¬ 
possible, as would also the other units of the movable base, if 


FLOATING DRYDOCKS. 


303 


so fitted, to many or most of which the present trolley system 

of transfeience would he of little or no use under any condi- 
tions. 

MAGAZINE AND EQUIPMENT SHIPS. 

No model n na\al war has witnessed the contingency of a 
vessel or fleet with exhausted ammunition and no supply at 
hand. It has seen operations against shore bp.tteries and forts 
cuitailed lest such a condition exist, and it has seen steel pro¬ 
jectiles used against fortifications when cast iron would have 
been moie economical and suitable. Although exhausted am¬ 
munition has not yet been recorded, it is still a highly possible 
contingency in a modern naval war. Rapid successive engage¬ 
ments may not be possible of avoidance when on the purely 
defensive, and successive victories may end in defeat and de¬ 
struction when ammunition fails. Years of peace are apt to 
cloud our sight to this contingency. Ordinarily the deteriora¬ 
tion of ammunition from age is our greatest concern, and tar¬ 
get practice gives no idea of the exhaustive hail of small-caliber 
shot that may be required to meet a well-directed and deter¬ 
mined attack of torpedo craft. The question of coal supply 
we can never avoid, but the question of exhausted ammunition 
when far from a base, v r e have yet to face. We may hope to 
secure coal by some means when far from a base, but available 
ammunition will never be captured, confiscated or bought, 
under like conditions. 

This possible condition of depleted or exhausted ammuni¬ 
tion of any or all calibers suggests a magazine ship as an im¬ 
portant unit of a movable base, and as a still more important 
naval adjunct, if of sufficient speed and capacity to become a 
flying sub-base. As the ammunition should be stowed below 
the water line, this vessel may at the same time become an 
equipment ship carrying such equipment stores above the 
water line as are most essential and most likely to need renewal. 

t 

RECRUITING AND HOSPITAL SHIPS. 

As a badly disabled man is of no value as a working unit on 
a fighting ship, it is highly important, both for his own com- 


304 


FLOATING DRYDOCKS. 


fort and the good of the ship, that he be removed as soon as 
possible and his place supplied with an able bodied man. 

As men ready and fit for service go to the fleet and the ill 
and disabled come from it, recruiting and hospital service can 
be combined to advantage on the same ship. Not all humani¬ 
tarians will agree to this proposition, as it will deprive the 
ship of the immunity enjoyed by a purely red-cross institution, 
but if the ship be given great speed it may readily avoid cap¬ 
ture and will the sooner bring the ill and disabled to greater 
comfort and the sooner supply their vacancies in the fleet. 

In emergency and particularly in the early stages of defen¬ 
sive operations, the recruiting and hospital ship may become 
of the greatest value for use as a transport. The prompt land¬ 
ing of a few hundred men before strong opposition from sea 
or land can be offered, may secure the rapid and safe estab¬ 
lishment of a movable base, or the successful holding of other 
important positions, which many times the same number oT 
men could not effect after a slight delay. 

The maintenance of hospital ships or of transports, alone, 
does not appeal to us in time of peace, therefore this class of 
sub-bases may ordinarily be usefully and constantly employed 
as training ships for landsmen, which will insure the readiness 
for use of these ships. 

THE COMPLETE BASE. 

The complete movable base consists, then, of floating dry-^ 
docks, repair ships, colliers, magazine and equipment ships, 
and recruiting and hospital ships, to which may be added 
provision, and refrigerating ships, and most of which may 
become transports to a greater or less extent in time of neces¬ 
sity. 

With the exception of the floating dock all of these units 
should be given great speed, and equipped with transferring 
devices so that they may become of the greatest possible effi¬ 
ciency as flying sub-bases. As there is a natural disinclination 
to put great value into a vessel for naval purposes which can¬ 
not fight, the sub-bases may be lightly armed with three and 


FLOATING DRYDOCKS. 


305 


foui inch calibers and smaller rapid-fire and automatic guns, 
thus protecting them to some extent, and rendering them most 
formidable commerce destroyers. 

Thei e is also farther reason for lightly arming these ves¬ 
sels. The movable base will be established as near the scene 
of operations as possible, perhaps in a hostile country itself. 
It is desirable to employ as few vessels of the fleet as possible 
m the protection of the base, and to this end more or less of 
the guns f 1 om the sub-bases may be landed and emplaced in 
shore batteries for protection both from land and seaward. 
One of our latest lessons in naval warfare is that land batteries 
are hard to silence and still harder to destroy, and that in 
closely engaging them a ship takes undue risk. With concrete 
and deflecting armor and the unlimited space afforded on 
shore, it seems a safe assertion to say that in a (few days a 
battery could be constructed that the heaviest guns afloat could 
not destroy. Deflecting armor and cement for concrete may 
readily be carried in abundance on the floating dock, as might 
also land and floating* pile drivers for farther aid in fortifica¬ 
tion work. If desired, a few larger caliber guns could be car¬ 
ried in storage on the dock for rendering shore batteries still 
more formidable. With the assistance of torpedoes, subma¬ 
rines and monitors, in conjunction with the shore batteries, 
the defense of the movable base could be made very formidable, 
and the cruising fleet would be left largely free for independ¬ 
ent operations. 

In the defense of the movable base it is important to note 
that its most essential unit, the floating dock, can be rendered 
nearly invulnerable by almost complete submergence. No 
more than a couple of feet of the side walls need be left above 
the water line, and should these be pierced, the dock can be 
readily and quickly raised a little higher and the shot holes 
stopped with plank and oakum. The accidental sinking of a 
floating dock may be prevented by placing a watertight deck 
in the side walls at a suitable height; in a military dock such 
a deck is advisable for the farther reason that docking opera¬ 
tions may’ be hastened by eliminating the necessity of skilful 
management when reaching deep submergence. 


20 


3°6 


FLOATING DRYDOCKS. 


Having the floating drydock as the essential unit, it is not 
absolutely necessary that the others should be the high speed, 
lightly-armed vessels that are herein advocated, in order to 
constitute a very efficient movable base for operations in one 
place without extended scope. Merchant vessels can be taken 
in emergency and converted to as great advantage as possible, 
and convoyed to the site of the base while the dock is being 
towed. The floating dock cannot, however, be left to be 
secured when the emergency occurs. Ordinarily it can be 
built in two years; under stress the usual types can be built 
in a year, and the sectional type can be built in six months by 
constructing the sections at different ship yards. 

AVAILABLE FLOATING DOCKS IN THE WORLD. 

The United States has a modern military floating dock at 
New Orleans of fifteen thousand tons capacity, but not equal 
to the heaviest ships it is building. It has a ten-thousand-ton 
dock at Pensacola, purchased from Spain, and of doubtful value 
for a movable base. In two years it will have in the Philip¬ 
pines the most complete military dock of modern times, of 
sixteen thousand tons capacity and equal to the heaviest ships 
it is building. j 

Great Britain has recently installed at Bermuda a floating 
dock of the same type as that at New Orleans, of nearly six¬ 
teen thousand tons capacity. 

Austria is building a floating dock of fifteen thousand tons 
capacity for the naval station at Pola. 

Spain has a new floating dock in the Mediterranean of 
twelve thousand tons capacity. 

In Germany there are commercial floating docks that are 
available for military operations. Four at Hamburg, of which 
one has a capacity of seventeen thousand five hundred tons, 
one a capacity of sixteen thousand tons, and the other two of 
lesser capacity. At Stettin there is a German dock of eleven 
thousand tons capacity. 

While the docks mentioned are mostly very able and efficient, 





FLOATING DRYDOCKS. 


307 


none of them have reached the state of development desirable 
in the basis of a movable base. 

COMPOSITION OF BASE. 

A complete and efficient movable base will consist of one 
floating - drydock, two repair ships, four colliers, two magazine 
and equipment ships, and two recruiting and hospital ships; 
the ships to be of the high-speed and lightly-armed type called 
flying sub-bases. For greatest safety in assembling at a 
selected location, transference to another locality, or general 
dispersal in emergency, the floating dock should consist of the 
sectional type in four sections, any three of which should be 
capable of lifting" the heaviest battle ship or the longest cruiser. 

The location of a temporary base having been selected, each 
section of the dock is taken in tow by one or more of the ship 
units and the base is proceeded to as expeditiously as possible. 
It has been demonstrated that a floating dock can be towed at 
an average rate of one hundred miles per day, and with the 
sectional type towed in sections by the powerful sub-bases, a 
greater speed might easily be reached. The arrival of three 
sections of the dock at the base is practically certain under any 
circumstances, especially if convoyed by war ships, and the 
arrival of all sections is almost sure, in which case the fourth 
section is available for the docking of tugs, torpedo boats, and 
other small craft. The movement of this base may be made 
as secret as possible, the various units departing from different 
permanent stations at various times and by various routes, or 
it may be made openly and advertised to the world, as circum¬ 
stances may indicate. 

When a movable base has been established in a hostile ter¬ 
ritory and war has fairly begun, its removal or dispersal will 
be more difficult of accomplishment than its assembling. The 
flying sub-bases may be able to care for themselves, but the 
slow-moving dock is less fortunate. A dock may, of course, 
be quickly destroyed in extremity and need never be captured, 
but destruction is an undesirable event. Here again the sec¬ 
tional dock offers the greatest possibilities. It may be moved, 


3°8 


FLOATING DRYDOCKS. 


one section at a time, in the face of possible detection, and op¬ 
position, as the capture of one section may well be risked, for 
it means no material benefit to the captor. 

constant use. 

The complete movable base will never be realized if it is to 
be purely a war luxury, and if reserved for that it might be of 
doubtful effectiveness when needed. Its units should be in con¬ 
stant use in order that we may be familiar with their handling 
and that they may be in a known state of efficiency. 

There is plenty of use for all the floating drydocks we may 
build, and as a peace tool they have many advantages over the 
land dock. When a new permanent base has been selected, a 
floating dock can be towed there and we are at once ready 
for the most important operation that is performed on a repair 
station. By taking a repair ship with it we have at once an 
effective shop, if the dock is not already fitted as such. 

The selection of a site for a land dock on a new station is not 
a matter to be quickly or lightly disposed of to the best ad¬ 
vantage, and the floating dock gives plenty of time for due 
consideration of the matter. Should the site selected for a 
new station prove undesirable or a more practicable one be 
found, there is far less to be abandoned if we have a floating 
dock that can be towed elsewhere. 

For cleaning, painting and light repairs, the floating dock is 
much more desirable than the land dock, as it brings the ship 
well above the water surface into light and air where opera¬ 
tions can be conducted with the greatest facility and effective¬ 
ness. As a ship has been cut in two, pulled apart thirty feet 
and lengthened in the center on a floating dock, there remains 
no doubt about what can be done on them in the way of heavy 
repairs. 

The docking of ships is at present confined to one small class 
of officers, but if floating docks are to be of any importance 
in future naval strategy, their use and operation should be 
familiar to every line officer, and is next in importance to a 
knowledge of steam engineering. 


floating drydocks. 


309 


The use and operation of a floating drydock is not compli¬ 
cated. When placed in the axis of a current the entering of a 
s ip is greatly .facilitated, its centering is an easy matter, and 
with our system of docking keels giving three lines of support 
on the bottom, its proper landing is very simple. Without 
other knowledge of the dock, if pumping is begun at the cen- 
ter compartments and continued towards the ends until the 
ship is out of water, no injurious strains will be'caused whose 
development would not be perfectly apparent to the eye in 
time to stop. There is less chance of injury in this class of 
docking, as two elastic and floating structures are coming in 
contact instead of an elastic and a fixed and rigid one. 

From a strategic point it is important that a standard type of 
dock be selected as soon as one can be determined on, so that 

when the officer has become familiar with one he will under¬ 
stand all. 

The constant use of floating drydocks can be assured, and 
the next consideration is the repair ship. It has been men¬ 
tioned how these ships can be of value in founding a new 
station, and they would be of farther value as a constant ad¬ 
junct to a squadron in foreign waters or during maneuvers. 
When a ship is injured at a distance from a repair station 
prompt aid may mean its salvation. 

Not the least valuable use of the repair ship in time of 
peace would be as a training ship for naval artisans. The 
training of a landsman to a seafaring man of ability, whether 
he be gun pointer, machinist, electrician or quartermaster, is a 
matter requiring care and consideration, and we have demon¬ 
strated that it can best be commenced on training ships. 

The constant use of colliers in time of peace needs little dis¬ 
cussion. At present we must, perforce, supply our fixed coal¬ 
ing stations from mercantile colliers on account of lack of 
naval colliers. Coaling at sea we only attempt as a maneuver 
on account of its present difficulties, and at times in foreign 
countries we may pay large prices for inferior fuel. Much of 
this could be remedied with a few suitable and well-equipped 
colliers of large capacity, and the service should not rest until 


3io 


FLOATING DRYDOCKS. 


some quick and certain method has been found for coaling 
ships at sea. 

It has already been mentioned how the recruiting and hos¬ 
pital ship may ordinarily be used as a training ship, and the 
same may be said for the use of the magazine and equipment 
ship. We are just emerging from the period when we had 
added fighting ships to our Navy until we had not only more 
than we could competently dock, but had many that we could 
not dock at all without civil aid, and at one time without for¬ 
eign aid. 

We are now entering, if we are not already in, the period 
when we will not have enough training ships to supply our 
squadrons with suitably broken-in landsmen who have had a 
chance to acquire a taste for the sea in some comfort and under 
conditions that would make them of the most value. 

* Aside from its value as a training ship, the presence of a 

magazine and equipment ship with a squadron, whose supply 
of ammunition would thus be greatly increased, would greatly 
augment its military value. 

As training ships, alone, there seems to be sufficient reason 
for the existence of the flying sub-bases. 

STRATEGIC VALUE. 

The movable base suggests, first and last, distant or foreign 
operations, but, considered from a purely defensive standpoint, 
it has a much more important value to the Navy. 

Our naval bases on the continent were established many 
years ago in the time of wooden sailing ships and short-range 
cast-iron guns. When established they were geographically 
unassailable, and strategically, fairly so for the times and cir¬ 
cumstances. With few exceptions, they are no longer unas¬ 
sailable. Were they all impregnable, they are too few and too 
poorly located for a satisfactory naval defense of our extensive 
coasts. 

When our land drydocks, under construction and projected, 
are all finished our docking facilities, considered from a de¬ 
fensive war basis, will still be greatly inadequate to our needs. 



FLOATING DRYDOCKS. ^II 

By placing a thoroughly-developed military floating dock at 
each of our naval bases, we may in time of threatened danger 
double out available bases on the coast by towing the docks to 
var ious points o t f vantage, or in the last extremity, if forced to 
retreat up our rivers and bays, we may take our floating docks 
with us and establish movable bases that will the sooner enable 
us to again reach our coasts. 


312 


FLOATING DRYDOCKS. 


t 


FLOATING DRYDOCK CONSTRUCTION.* 
By Wm. T. Donnelly, Mem. B. E. C. 

Presented January 12, 1905. 


I have considered the subject under several general heads 
so as to give some comprehensive idea of it to those entirely 
unfamiliar with it, and then to go into the details of the con¬ 
struction of large floating docks, which will be of more interest 
to those already familiar or interested in the particular line of 
engineering. 

With the aid of the slides which I have prepared I shall first 
endeavor to give a general idea of what a floating drydock is. 

This slide (see Fig. 1) shows a io,ooo-ton floating drydock 
with a large steamer upon it, the Fall River Liner Priscilla, 
with which you are all probably familiar. 

A floating drydock, as you will readily see, is a large float¬ 
ing structure, so large that it can not only float itself, but the 
largest vessel for which it is designed. 

The steamer you see here is 440 feet long, 92 feet wide over 
the guards and has a draught of about 16 feet. The dock is 
468 feet long and is composed of five sections or separate float¬ 
ing parts which are connected together and operated as one; 
these sections will be fully explained later. 

The manner of getting this ship upon the dock was as fol¬ 
lows: You will notice that on each side of the boat the dock 
has high, narrow sides which come above the water line of the 
boat, and you will readily understand that these sides, which 
carry the machinery, could be above the water, while the cen¬ 
tral part of the dock was far enough below the surface to 

* Reprinted by permission from the Brooklyn Engineers’ Club Proceedings for 
1905. 





Fig. l io,ooo-Ton, Lang Balanced Sectional Floating Drydock. 
Tietjen & Lang Drydock Co., Hoboken, N. J. 


Face p. 312 
























A Adamson. 

Floating DsyJJccJtr. 

Patented Pec. /J, /s/6. 




Fig. 2.— First Patent for a Floating Drydock in the U. S. 














































































A. LINCOLN. 

MANNER OF BOTTYING VESSELS. 

No. 6,469. Patented May 22, 1849, 



Fig. 3. —Patent Granted to Abraham Lincoln. 







































































































FLOATING DRYDOCKS. 


3 X 5 


allow the steamer to float in between them. Much the larger 
part of this dock is now below the surface of the water and 
is in the form of a large hollow box connecting the two high 
sides. All the different divisions of the dock are provided 
with means for letting in water and for taking it out. 

• The operation qf this dock is as follows: 

When the steamer was approaching to be docked, the dry- 
dock was about at the level that you now see it, but, of course, 
the space between the high sides was vacant and all that you 
would see would be a long line of keel blocks down the cen¬ 
ter (some of which you can now see in front of the boat) ; 
those on which the steamer was to rest had all been carefully 
arranged to correspond with the keel of the boat, and certain 
blocks on each side, known as bilge blocks, had also been 
arranged. About the time when the steamer first came in 
sight the dockmaster gave instructions to open the flood gates. 
As soon as this was done, the water commenced to flow into 
the dock from the outside and the dock commenced to sink, 
the water flowed over the deck, then covered the keel and bilge 
blocks until nothing was left above the water but a long, nar¬ 
row strip on either side. When the dock had settled until 
there was about a foot more water above the keel blocks than 
the draught of this steamer, the flood gates were closed and 
the dock floated quietly. Then word was signaled to the 
steamer, which in the meantime had come up, and, if under 
steam, she steamed in or was pushed in by a tug, or perhaps 
was pulled in by her windlass engine hauling on the line, which 
you can see reaching from her hawse hole to the mooring post 
on the pier. When the steamer had been carefully located 
directly above the keel blocks which had been arranged to carry 
her, the machinery for removing the water was operated, and 
just as the letting in of water caused the dock to descend, the 
removal caused the dock to ascend, at first slowly, until the 
long line of keel blocks gently touched the bottom off the 
steamer. When firmly grounded on these the bilge blocks were 
drawn. This means that a certain number of blocks which 
have been arranged to support the vessel under each bilge or 


3 t 6 


FLOATING DRYDOCKS. 


side are pulled inward from each side of the dock towards the 
center until they touch the steamer, and act both as side sup¬ 
ports and props to keep the vessel upright as she rises out of 
the water. When this was accomplished, the machinery was 
operated more rapidly and the dock and vessel, which now 
became like one structure, rose together out of the water. 
The time from the location of the steamer in the dock until 
she was raised entirely out of the water, as shown, was about 
45 minutes. 

I will next take up the historical side or the development of 
floating drydocks in the United States. 

The floating drydock is generally considered to be an 
American invention, and this would seem to be probable from 
this slide, which you will see (see Fig. 2) is taken -from a 
patent issued to J. Adamson in 1816. 

This is one of the first patents issued by the United States, 
and was at a time when the patents were so few that the Gov¬ 
ernment had not discovered the necessity of giving each a 
number. 

You will see that at this time a floating dock was a very 
simple structure. It is evident from a little study of this draw¬ 
ing that the idea originated from the wreck of an old hull 
laying on some sloping beach, which was used by cutting out 
the stern and making gates to close the opening, similar to 
those of a canal lock. When the gates were open and the water 
admitted, the structure rested upon the bottom, and at high 
tide the boat to be docked was floated in and located. As the 
tide receded the water left the dock, and when it was all out 
the gates were closed and its return was prevented. You will 
see at each side in the plan view that pumps are provided which 
were operated by hand. It is most probable that these were 
only intended to take care of the leakage. It is evident that 
this is not, strictly speaking, a floating drydock, as it was evi¬ 
dently intended to rest on the bottom, but, as you will under¬ 
stand, at an extra high tide it must either fill over the sides or 
float, and at some time became the first floating drydock, prob¬ 
ably against the will rather than from the intent of the in- 


FLOATING DRYDOCKS. 


317 


\ entoi. Old as this form of dock is and limited as is its 
use, there was within a few years one of precisely this con¬ 
struction in use in Weehawken Cove, Hoboken, for the dry¬ 
docking and repairing o,f canal boats. 


The next slide (see Fig. 3) shows the germ of another line 
o thought which has relation to the development of floating 
dry-locks- This shows, as far as I am aware, the only re¬ 
corded invention by a President of the United States, as you 
see this is a patent granted to Abraham Lincoln in 1840. 
From the “Life of Lincoln” we learn that about this time he 
made a trip on a flat boat down the Ohio and the Mississippi 
Riveis, and it was undoubtedly his experience with sand bars 
and shoals on this trip that was the occasion of this invention, 
which is in the nature of additional buoyancy carried on each 
side of a boat to be used in water too shallow to float the 
vessel. The intention evidently was to lower the long hollow 
boxes, which you see on each side, into the water, and then to 
force them down into the water by means of ropes and frame¬ 
work. I am not aware that this invention ever came into 


use, and its inventor certainly had other and more weighty mat- 
ters to think of in after years. 


With the next slide (see Fig-. 4) we come to the first large 
floating dock which was built in this port and is the oldest float¬ 
ing drydock now in use, and can be seen at the Erie Basin, 
Brooklyn. As originally constructed, this dock had a gate at 
each end, which was intended to operate after the principle of 
the dock invented by Adamson, but when completed it was 
found impossible to use it in that way. The reasons which 
led to its failure I will explain later when I come to describe 
the operation of the various forms of floating docks. This 
was, at the time of its construction, between 1845 and 1850, 
a very large structure, and it remains today the largest single 
structure in wood that has been undertaken for a floating dock. 
It is 330 feet long by 100 feet wide. It is known as the Old 
Balanced or Box Dock. 


This slide (Fig. 5) shows the next development of the float¬ 
ing dock. When it was found impossible to handle a single 


4 


318 


FLOATING DRYDOCKS. 


large floating structure with a ship upon it, the development 
took an opposite turn, and a number of small floating struc¬ 
tures were built, to be connected and used together, and this 
form of dock had been known as a “Sectional Floating Dock.” 
You will see that it is composed of a number of separate float¬ 
ing sections connected together on each side by locking logs, 
which are designed to permit a limited amount of motion be¬ 
tween the sections while keeping them in alignment, particur 
larly while sinking. The flexibility or movement between the 
sections made it necessary to provide some flexible means of 























































































FLOATING DRYDOCKS. 


319 


transmitting power from one section to the others, and for this 
pui pose a double universal joint, with a slip or extension joint 
between, was invented. This will be more fully explained later. 
This dock, while having many undesirable features, was found 
to be veiy practical, and large numbers of them were built. 
The dock heie shown has four sections. They have been built 
with from three to seven sections, which, with a section of 
about 25 feet in length, gave a dock about 200 feet in length, 

n 


tr 



**•« 

l 

V 


\ 

; \\ 

r 



s 





tTJ 

urn 





Fig. 5 .—Old Sectional Dock. 

allowing for a short distance between the sections and a prow 
or overhang at each end. 

The next type to which I will call your attention is shown 
on this slide (Fig. 6). This is known as a Dodge-Burgess 
Sectional Floating Dock and was the subject of a joint patent 
to them under date of October 9th, 1841. 

The general arrangement of this dock is a number of pon¬ 
toons, ten, as here shown, arranged and connected together as 
































































































3 20 


FLOATING DRYDOCKS. 


in a sectional dock by a locking log, but in this dock the 
wings are absent, as you will see in the cross-section, and in 
their place there is only a framework, upon the top of which 



the machinery house is carried. This framework is attached 
to the central pontoon and raises and lowers with it. 

At each side in the cross-sectional view, directly below the 
machinery houses, you will see a ballast tank. This tank al¬ 
ways remains at the surface of the water, and is for the pur- 






























































































































floating drydocks. 


321 


pose of controlling the equilibrium of the lifting pontoon while 
submerged. The pumping of this dock is by machinery car¬ 
ried upon the top of the framework, and the power is dis- 
tributed along the top by a shaft with flexible couplings, in the 
same manner as previously described for the sectional dock. 




This type of floating dock was the largest that had been 
built in this country up to a very recent date, and is probably 
the most familiar, as two of these docks were located upon 
the New York water front, near Catherine Street Ferry, for 
many years. 







































































322 


FLOATING DRYDOCKS. 


The larger one was composed of eleven sections, each 30 
feet long by 100 feet wide, it being understood that I speak 
of the length as 30 ,feet from the fact that this is the dimen¬ 
sion which forms a portion of the length of the dock when con¬ 
sidered as a whole. These sections, with the space allowed be¬ 
tween them, made a dock about 350 feet long, having a lifting 
power of about 3,500 tons. 

This slide (Fig. 7) shows the next development. This form 
is known as a box or balanced dock. As you will readily see, 
it was built in one piece, and, to overcome the difficulties oc¬ 
casioned by the flow of the water from one end of the interior 
to the other, the cross-bulkheads, which are watertight, were 
added. These cross-bulkheads, four in number in this case, 
together with the center longitudinal bulkhead, divide the dock 
into ten independent watertight compartments, and, by means 
of gates which control the flow of the water from all of these 
to the pumps it is possible to control or balance the dock and 
ship. 

The building of docks of this type commenced about the 
close of the Civil War, and their construction continues at the 
present time ; the small and moderate sized are the most popu¬ 
lar, and there are undoubtedly more of these docks, ranging in 
capacity from 500 to 3,000 tons, in the waters of the United 
States than all other kinds taken together. This dock answers 
all the requirements up to a length approaching 300 feet. At 
about this length the proportion of length to depth is so great 
that it becomes impracticable to obtain sufficient longitudinal 
rigidity with wood as a structural material. A combination of 
wood and iron has been tried, but with very unsatisfactory re¬ 
sults. The cost of a steel dock of this type is so much greater 
than one of wood, and its prospective cost of maintenance so 
much more, as to deter any attempt in that direction for com¬ 
mercial purposes up to the present time. 

I will now pass to the most recent development and largest 
type of floating dock for commercial purposes in use in this 
country. This slide (Fig. 8) shows a balanced sectional float¬ 
ing drydock. Each of these sections, of which there are five. 


FLOATING DRYDOCKS. 


323 


possess all. the advantages of a box dock, that is to say, cross 
and longitudinal bulkheads and separate gates and independent 
means of admitting and removing water. Besides these there 
are added all the advantages of the sectional dock, such as the 
freedom from internal longitudinal strains and self-docking, 
which is a very important consideration in large docks. 

1 he pumping machinery consists of a boiler and engine on 
each side of the dock. These operate a line shaft provided with 
flexible connections between the sections. This line shaft oper¬ 
ates through intermediate gearing two pumps in each water¬ 
tight division of each section. As each section is divided into 
six compartments and there are five sections, there are sixty 
pumps. 

The dimensions of this dock are 468 feet long on keel blocks 
bv no feet wide over all. The height of the wings are suffi¬ 
cient to take a draught of 21 feet over 3-foot keel blocks. The 
lifting capacity is 10,000 tons, or about three times the size of 
the largest commercial floating dock previously built in this 
country. 

It is a most remarkable fact that from the building of the 
two Dodge-Burgess Sectional Docks, between 1850 and i860, 
to the building of this dock in 1899, there was no large float¬ 
ing dock built in this country, and this is still more remarkable 
when it is considered that there was a constant growth in the 
shipping and a real demand for larger floating docks. 

We will now pass to some illustrations of these docks in use. 

This slide (Fig. 9) shows a partial view of the dock last 
referred to, with the vacht Niagara, owned by Howard Gould, 
on the right, and a box dock on the left with the Corsair, owned 
by J. P. Morgan. 

Here you can see that a floating dock lifts a vessel up out of 
the water almost to the level of the pier or wharf, and also 
how the scaffolding is rigged for cleaning and painting. You 
will understand that this scaffolding around a vessel in dry- 
dock is the rule rather than the exception, as all work other 
than upon the under body or those parts below the water line 
is done while the boat is afloat, and, as the expense of’keeping 


























































































Yacht “Corsair.” 

J. P. Morgan, Owner. 


Fig. 9. Yacht “Niagara.” 

Howard Goued, Owner. 


Face p. 324 


























Fig. 10. —2,ooo-Ton Balanced Floating Dock, 
James Tregarthen & Son, N. Y. 


Face p. 325. 















FLOATING DRYDOCKS. 


325 


a vessel in drydock is considerable, every possible facility is 
provided to execute the work in a short time, both by appli¬ 
ances and laige numbers of men employed. The wooden horses 
seen in the foreground on the pier are carefully designed to be 
strong and light, so that they may be readily carried off and 
on the dock, and at each side there are uprights hinged to the 
deck of the dock, which, when not in use, rest against the side, 
as some are seen on the left of the Niagara. On the right of 
the pictuie, further down the dock, they can be seen in an 
upright position, secured by iron braces. On one side they have 
a series of pins which support one end of the scaffolding poles, 
the other ends of which are carried by ropes, called “slings,” 
from the side of the vessel. Below this scaffolding can be seen 1 
the wooden horses with planks upon them. 

The next slide (Fig. 10) shows a good sample of a large 
box dock of recent design and construction. This dock was 
built by James Tregarten & Sons and is now in use in their 
yard, foot of Seventh Street, East River, New York. It is 
about 2,000 tons capacity, the length on keel blocks is 260 
feet, length of box 186 feet 4 inches, and width over all 85 
feet. The pumping machinery is operated by electricity, the 
motor being* located and controlled in the small house seen on 
the right-hand wing. The current is led from a post on the 
pier by a flexible conductor. The type of sailing vessel which 
is shown on this dock is fast disappearing* from our waters, 
and from keel to truck is worthy of attention as illustrating 
marine practice of the past. This plate shows particularly well 
the keel blocks upon which the keel rests, also the bilge blocks 
in use to support the vessel in an upright position and those 
not in use drawn back out of the way on the right. The lines 
or ropes for operating these blocks are also plainly shown lead¬ 
ing up to the top of the wings. 

The next slide (Fig. 11) shows a smaller box dock of 
about 1,500 tons capacity. This dock is 130 feet long in the 
box and 190 feet long on the keel blocks, and has a width over 
all of 68 feet, and will take a draught of 17 feet above 3-foot 
keel blocks. The body of this dock is ] o feet 6 inches deep, 


FLOATING DRYDOCKS. 


326 

which gives it a very large lifting power for its dimensions. 
The design was developed particularly for the largest class of 
ocean-going tugs having large concentrated weights. The ma¬ 
chinery is operated by electricity, and the handling of the 
motor is from the small house seen at the left on the pier. 
This enables the dockmaster to direct the location of the ves¬ 
sel upon the blocks and to start, stop and regulate the speed 
of the pumping himself, thus dispensing entirely with an en¬ 
gineer. Keel blocks, bilge blocks and scaffolding are all very 
clearly shown in this slide. 

The next slide (Fig. 12) shows a basin dock. I show this 
for the purpose of comparison, so that those who are unfa¬ 
miliar with the subject may readily understand how a float¬ 
ing drydock differs from a basin drydock. You will here see 
what appears to be a large opening or basin extending from 
the surface of the ground to a distance below the surface of 
the water corresponding to the greatest draught of vessel which 
it is intended to accommodate. The sides and bottom are made 
to exclude the water, and a gate which is removable is fitted 
across the entrance. 

When the dock is full of water this gate is removed and the 
vessel to be docked enters and is located over keel and bil^-e 
blocks in the same manner as on the floating dock. Then the 
gate is replaced across the entrance and the pumping machin¬ 
ery is started, and, as the water is gradually removed, the ves¬ 
sel settles down upon the blocks. In this view the Shamrock 
II, well known as a contestant for the America’s cup, is shown. 

While basin docks have been built to very much larger size 
than floating docks, on the other hand floating docks have been 
built in much larger numbers, and are generally conceded to 
be much more handy and workable than basin docks. 

OPERATION OF FLOATING DRYDOCKS. 

We will now take up the operation of floating drydocks along 
lines which will be of more particular interest to those who are 
already familiar with the subject. 

This slide (Fig. 2) shows the first form of drydock of which 



Fig. 11. —Box Dock, Electric Driven Machinery. 



Fig. 


12.— Basin Drydock, Erie Basin, 
Yacht “Shamrock, 2d.” 


Brooklyn. 


Face p 326. 
























FLOATING DRYDOCKS. 


327 


M e ha\e any record in this country. As previously explained, 
if this drydock can be grounded or rest upon the bottom when 
being pumped out, and if it does not float until it is practi¬ 
cally empty, it will operate all right, but if any considerable 
amount of water is present at the time it floats, one end will 
certainly be slightly heavier than the other, consequently this 
end will sag down and the water will flow towards the lower 
end, causing it to still further settle, and any considerable 
angle of inclination would be liable to cause the displacement 
of the vessel upon the blocks. 

This slide (Fig. 4) shows the old balance dock now in use 
in the Erie Basin. I think this is the oldest dock now in use 
in the harbor ; as originally built, it had gates at each end simi¬ 
lar to those referred to in previous section on the Adamson 
dock, from which it was undoubtedly an outgrowth, and, so 
far as I am able to learn, the builders believed that they would 
be able to operate it entirely as a floating structure without 
resting upon the bottom at any time. 

The operation of this dock was intended to be as follows: 
The gates at one or both ends were opened and water was ad¬ 
mitted into the body of the dock, and it was sunken low. enough 
for the vessel to be moved in; after the vessel was in place 
the gates were closed at both ends and pumping commenced, 
the idea being to remove the water between the side walls and 
end gates, but, as there were no divisions, either longitudinally 
or laterally, to confine the water, as soon as pumping was com¬ 
menced the water would flow to the lowest end or side, and it 
was found impossible to keep the dock and vessel in a horizontal 
position. The gates were then abandoned and the attempt 
made to operate the dock as a box or balance dock, and in 
this connection I wish to call your attention especially to the 
arrangement of the pumping machinery. As you will readily 
see, there was a boiler and engine and a group of pumps at 
the center of each side of the dock. The pumps all draw their 
water from a central well or compartment. This compartment 
was connected to the various other divisions of the dock by 
gates as shown. The general plan of pumping was to start 


328 


FLOATING DRVDOCKS. 


all the pumps and lower the level of the water in the pumping 
compartment and then to open the gates from the end com¬ 
partment and allow the water to flow by gravity to the pump¬ 
ing compartment. This, you will readily understand, would 
work out properly if the dock was always on a perfectly level 
keel, but if for any reason one end became lower than the 
other, the delivery of water from that end would not be as 
rapid, and the subsequent pumping would tend to increase the 
difficulty, and the only method of correcting this condition 
would be to stop pumping, close all gates and admit water 
from the outside of the dock to the high end or side and then 
commence pumping over again. 

It was soon discovered that the only possible way to handle 
this dock was to place the vessel, whatever her length, in the 
center of the dock and then to pump all compartments at the 
same rate, stopping to correct any tendency to roll as soon as 
it became apparent. The continual docking of vessels shorter 
than the total length Qf the dock has resulted in straining the 
dock to such an extent that the center of the dock, longitudi¬ 
nally, is now about 4 feet lower than the ends. The dimen¬ 
sions of this dock, 300 feet long by 100 feet wide, in a single 
structure are such that it has never been possible to entirelv 
remove it from the water, and it is certainly remarkable that 
after more than fifty years it is still possible to dock vessels 
upon it. 

This slide (Fig. 5) shows the next development, which is 
the small sectional dock, commonly so called. In this dock the 
sections were made small enough to be controlled in sinking by 
locking logs connecting them; when a vessel is in place the 
vessel itself serves as the connection between the sections to 
steady and maintain them in correct relative position. The 
sections of this type of dock were made about 20 feet in the 
direction corresponding to the length of the dock and of a 
width proportionate to the length of the dock,^o as to give 
working room on each side of the largest vessel the dock would 
take. The machinery was placed on one side of the dock, with 
a water connection or leader extending through the center bulk¬ 
head to the other side. 


FLOATING DRYDOCKS. 


329 


As this was the first type of floating dock to be extensively 
used, and as it embodies most of the principles that are in use 
in the more recent and larger docks, I will try and explain the 
method of pumping and handling somewhat in detail. You 
will see by referring to the plans, Fig. 5, a dock of five sec¬ 
tions, which was quite a common number; these plans repre¬ 
sent a dock, each section of which is about 20 feet long by 
about 60 feet wide. You will understand that we speak of 
the shorter dimension of the section (20 feet) as the length, 
because it is that dimension which forms part of the longi¬ 
tudinal dimension of the dock as a whole. 

Each section was divided at a point corresponding to the 
center line of the dock by a watertight bulkhead. At the ex¬ 
treme outside of each section there was a flood gate. 

The pumping machinery was located on one side of the dock, 
and as it was necessary to bring the water from the other side 
beyond the center bulkhead, a leader or pipe was provided, the 
flow through which was controlled by a gate or valve similar to 
the flood gates. The pumping machinery consisted of four 
single-acting pumps for each section, and were operated 
through rocker arms, connecting rods and shafting, as shown 
in Fig. 5. To allow for movement between sections, the con¬ 
nection of the power from one section to the next was made 
by a combined double-universal and slip joint. This mechanism 
permitted a considerable movement in any direction without 
interfering with the transmission of the power. 

To limit the movement of the sections there was provided 
on each side at the junction of the wings with the deck a con¬ 
tinuous locking log which passed through strong keepers near 
each end of each section. These logs were not intended to take 
any of the strain of lifting the vessel, but were to control and 
keep in alignment the sections while being lowered and until 
the vessel was firmly resting upon the blocks, when it will be 
readily understood that the vessel herself would make a firm 
and strong bond between the sections. 

Power was furnished for pumping by a boiler and engine 
located on the middle section. 


330 


FLOATING DRYDOCKS 


The operation of the dock was about as follows: The keel 
and bilge blocks having been prepared for the vessel to be 
docked, all the flood gates are opened about half way and the 
entering water causes the dock to settle; any tendency for one 
section or part of the dock to descend faster than the other 
is corrected by slightly closing the corresponding gate. When 
the deck of the dock approaches the surface the gates are grad¬ 
ually closed, and, as the water floods the dock between the 
wings, the different sections and the dock as a whole are care¬ 
fully leveled. 

This is quite important to insure complete control of the 
dock. When the deck is entirely submerged the flood gates are 
opened wider and the dock descends to the necessary depth to 
allow the vessel to enter over the blocks. At this depth all 
valves are closed and the vessel is moved and correctly located 
over the blocking and secured bv lines at bow and stern to the 
sides or wings of the dock. The pumping machinery is then 
operated, slowly at first, to bring the keel blocks gently against 
the keel of the vessel without disturbing them. As soon as 
the dock is pressed firmly against the bottom of the vessel the 
bilge blocks are drawn under the bilges. This may be done 
while the pumping is going on slowly, or if the vessel is large 
the pumping is stopped while the blocks are drawn. When 
this is accomplished the pumping machinery is speeded up and 
the water removed more rapidly. The dockmaster in the 
meantime watches the dock and vessel, and if for any cause 
there is a tendency for one side or end of the dock to rise 
faster than the other, he does not change the rate of pumping, 
but causes water to be let into the section or side which is com¬ 
ing up ahead or faster than the other. 

Of course, if the vessel is not as long as the dock or does 
not rest evenly upon all the sections, those not supporting the 
vessel will naturally rise faster than those that are to support 
the vessel, and from the beginning of the pumping it will be 
necessary to check their rise by admitting water. 

When the pumping commenced, the level of the water in the 
interior of the dock was approximately that upon the outside, 


FLOATING DRYDOCKS. 


331 


and consequently the pumping machinery would be required to 
<teli\ei the water only at a slight elevation above that from 
\\hich it was received, and the load upon the engine at this 
time is small, hut at this time the water is being removed from 
the wings only, and as the area or bulk of these wings (exclus¬ 
ive of the pump wells, which do not assist, as they are full of 
■\\atei at all times while the dock is submerged) is small com¬ 
paratively to the area or bulk of the vessel at the water line, 
the vessel raises slowly, while the difference between the inside 
and outside level of the water in the dock changes rapidly, thus 
increasing the load upon the pumping plant. This will con¬ 
tinue until the interior level of the water (that in the interior 
of the dock) has been lowered down to the level of the deck. 
At this time, with such a dock as the one referred to, with 
a vessel of the full capacity of the dock upon it, drawing when 
afloat, say, 12 feet, will have been lifted 3 feet and the interior 
water level, which at the start was about 2 feet below the ex¬ 
terior, has been increased to a difference of 12 feet. 

When the interior water level reaches the level of the deck 
of the dock a very marked change takes place in the condi¬ 
tions. I he area to be pumped at once increases to the entire 
area of the dock and is many times more than the correspond¬ 
ing area of the vessel, which, in fact, is rapidly decreasing. 
The necessary consequence is that the vessel and dock from 
this time on rise out the water much faster than the reduction 
of the interior water level, and the head against which the 
pumps are required to deliver the water rapidly falls with a 
corresponding decrease of the load on the engine. If we con¬ 
sider this dock as having a depth in the body of 8 feet and that 
at the time the deck of the dock reaches the water that there 
is 1 foot of water remaining in the dock, then the head against 
which the pumps will be delivering at this time will be 7 feet, 
a decrease of almost one-half from the maximum head of 12 
feet. 

With the deck o>f the dock at the surface of the water an¬ 
other marked change takes place. If the vessel being raised 
has occupied only four sections, the fifth section will now have 


332 


FLOATING DRYDOCKS. 


in it about 7 feet of water, or the flood gates of this section 
have been so regulated that the interior water level is only 1 
foot below the exterior, but from this point, or, as we say, when 
the water leaves the deck of the dock, it is necessary to pump all 
sections, both loaded and unloaded alike. 

The lack of comprehension and grasp of the principles of 
hydraulics as applicable to these structures has resulted in a 
general mistrust which is not warranted. 

With the deck of the dock flush with the surface of the 
water, I would like to call your attention to some of the con- 
siderations of stability of dock and vessel. 

As you are well aware, a vessel when afloat without cargo 
(which is the usual case when drydocking is to he done) is in 
a condition of minimum stability, and that this stability will 
rapidly disappear as the vessel raises from the water. There¬ 
fore it is necessary in drydocking a vessel in a floating dry- 
dock to make some provision for the stability of dock and ves¬ 
sel as they rise together out of the water. The stability of 
the vessel relative to the dock is provided for by the bilge 
blocks which are drawn under the bilges (corresponding to 
the widest part of the bottom of the ship) before she is lifted 
any considerable distance, hut as soon as this is done the 
drydock must assume the double responsibility of caring 
for itself and the vessel also. 

The wings of a floating drydock are often considered as 
serving only to carry the pumping machinery, but this is far 
from the fact. Their most important use is to furnish sta¬ 
bility for the vessel and dock as they rise out of the water. 

The details of this problem are too intricate and involved 
to be considered at this time, but if you will consider the fact 
that stability in its last analysis depends upon turning moment 
applied to the floating mass, you will at once see that the wings 
of a floating dock situated at a considerable distance from the 
center line of the dock and vessel considered as a single float¬ 
ing structure are admirably placed to counteract the loss of 
stability of the vessel as she rises out of the water. Further 
than that I would state that the proportions are such in a 





o/raj 


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f 

i i 


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j < 

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2 


j 

1 

'o 

V 


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Fig. 13 . — Cross-Sectional Elevation Plan of Box or Balanced Drydock. 





















































































































































































































334 


FLOATING DRYDOCKS. 


properly-designed dock that the combined stability of dock and 
vessel are at all times more than the stability of the vessel 
when afloat. 

From the consideration of this dock we will pass to the 
next development, or the “box or balanced dock,” as illus¬ 
trated by this slide (see Fig. 7). As has been previously 
stated, this dock is the type which is the most popular at 
this time for small and moderate sizes, or from 500 to 3,000 
tons capacity. 

The special features of construction of this dock are a 
single rigid structure, a center longitudinal watertight bulk¬ 
head and a number of watertight transverse bulkheads, divid¬ 
ing the dock into a sufficient number of separate compart¬ 
ments so that the controllable pumping may control the action 
of the dock. The machinery of these docks is located on one 
side only and the water from the opposite side is secured by 
leaders and control valves in the same manner as described 
for the sectional docks. The flooding and sinking of the dock 
is also carried out in the same manner, care being taken in 
sinking to have the water come over the deck at each end 
slowly and as evenly as possible. The vessel, when smaller 
than the capacity of the dock, should always be located near 
one end, and the pumping regulated by the flood gates so as 
to bring up the dock on an even keel, both transversely and 
longitudinally. 

As to the particular construction of one of these docks, I 
would call your attention to this slide (Fig. 13), which shows 
a working drawing, a cross-section, of a recently-designed dock 
of about 1,500 tons capacity. From this you will see that 
the width is 68 feet and the depth at the center correspond¬ 
ing to the longitudinal center line is 10 feet 8 inches, and 
the entire depth, including the wing, is 32 feet it inches. The 
distribution and dimensions of the timber is so .fullv given 
as to need little explanation. You will notice a second longi¬ 
tudinal bulkhead on each side of the center to give longitu- 
dinal rigidity. This slide (Fig. 14) shows a side elevation 
and plan of the same dock. In these views the location and 


< 




































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































FLOATING DRYDOCKS. 


335 


construction of the pumps is very clearly shown. There are 
t\\ ent\ pumps located in three pump wells on one side of the 
dock. On the opposite side will be seen three similar pump 
wells, but without pumps. The object of these pump wells 
is to equalize the buoyancy on each side of the dock, as the 
pump-v ell space does not assist m lifting - . 1 lie construction 
of the prow or outrigger on each end is here quite clearly 
shown, also the opening in its center to allow for the lowering 
of the rudder of vessels when on the dock. 

\\ e will now pass to the most recent type of floating dry- 
dock, illustrating the largest development in the commercial 
floating dock in this country up to the present time. (See 
Fig. 8.) This slide shows a balanced sectional drydock o,f 
five sections, having an overall length of 468 feet, a width 
of no feet 10 inches, and a lifting capacity of 10,000 tons. 
The arrangement of sections, locking logs, bulkheads and 
pumping machinery is clearly shown. There are thirty pumps 
on each side, and the manner in which they are operated is 
quite clearly shown in Fig*. 16. 

This type of dock is the invention of Mr. Frederic C. Lang, 
and patents were issued to him under dates of April 10th and 
August 21, 1900. As we have followed the developments of 
these structures, it will seem to most of you that this dock 
is so much a development out of the previous structures that 
its production called for little invention, but this view is op¬ 
posed to the most positive evidence to the effect that there was 
a real and well-known demand for a large floating dock in 
this port for more than twenty years. I11 fact, the two Dodge- 
Burgess docks of 3,000 and 3,500 tons, previously referred 
to, were the largest in existence in this country, and no actual 
advance had been made in fifty years. 

When, in the early part of 1900, the proposition of con¬ 
structing* a io,ooo-ton floating drydock was first brought to 
the attention of the engineering firm with which I was con¬ 
nected (Faber du Faur & Donnelly), and I became convinced 
that in connection with the development of an entirely new 
plan of construction an increase of size of about three times 


336 


FLOATING DRYDOCKS. 



over any previous wooden floating drydock was to be under¬ 
taken, you will readily understand that the situation called for 
serious thinking, particularly as the next largest work in this 
line was about fifty years old. 

Much of the unqualified success of the undertaking, even 
from an engineering point of view, is due to the inventor, 
Mr. Frederic C. Lang, and his long experience in the build¬ 
ing and operating of the different types of smaller docks; 
from years of experience in handling them as a dockmaster 
he was in possession of a knowledge of all the conditions 
which such a structure must meet. During the designing, one 
of the first features which received consideration was the 
relative advantage of wood-and-steel construction. After a 
careful investigation, somewhat to my surprise, I am free to 
admit, wood won out upon its merits, and when the reduction 
of first cost is also made an element the comparison becomes 
impossible, as the cost of a steel dock of this size is almost, 
if not quite, twice as much as one of wood. As to durability, 
it would seem as if little could be asked in that direction with 
the evidence before us of the three largest floating dock 9 


Fig. 15 .— Transverse Section of Wooden Drydock, Showing Truss. 























































































FLOATING DRYDOCKS. 


337 


in the port, each of which is about fifty years of age. Some 
one may ask if the original wood of these docks has not been 
replaced, perhaps several times, in that time. To this I would 
answer that the most careful investigation on my part has 
failed to discover any evidence of any such change of timber 
in the body of the dock or the trusses which support the weight 
of the ship. 

In the upper work, which has been exposed to the sun and 
weather, there has been considerable replacing of material. 

To protect these wooden structures below water from the 
attacks of worms and the teredo it is the practice to treat the 
bottom and sides with a coat of coal tar, then sheath them 
with hair felt saturated with creosote, and this with a covering 
of i-inch rough boards treated with creosote and arsenic. A 
dock prepared in this manner may remain in the water almost 
indefinitely. 

The design of the truss used is clearly shown on this slide 
(Fig. 15). Here you will see a half cross-sectional view of 
the dock. The length o ( f the trusses was no feet and the 
depth 12 feet 2 inches. The upper and lower members of the 
truss passed through the center bulkhead and the longer diago¬ 
nal braces met in the center. The shorter braces abut against 
the center bulkhead on opposite sides. 

The center bulkhead was watertight, as previously described; 
on each side there were three additional bulkheads to stiffen 
the dock longitudinally. These were not made watertight. The 
members of the truss were proportioned for a maximum strain 
of 1,000 pounds per square inch tensile and compression. 

The distribution of the strains in a dock of this kind are 
somewhat peculiar. The first pumping removes water only 
from the wings located at each end of the trusses, and, with 
the vessel resting only on the keel blocks at the center of the 
dock, we have a beam loaded at the center and the force ap¬ 
plied at the ends. 

When the vessel is entirely raised, the wings not only do not 
support any of the burden, but themselves act as a reverse 
load upon the trusses, and the weight of the ship is almost 


22 


33 « 


FLOATING DRYDOCKS. 


entirely borne by that portion of the trusses between the wings. 
Careful investigation of these conditions develop the curious 
fact that under some conditions of use the greater strain upon 
the trusses will be produced by a part of the vessel’s weight 
acting through the buoyancy of the wings upon the ends of the 
trusses. 

This slide (see Fig. 16) also shows the general arrangement 
of the pumps, also details of the flood gates and pump buckets. 

The pumps were arranged in groups as shown in Fig. 8. 
Referring to Fig. 16, it will be seen that the pump well has 
a watertight floor at about the level of the deck of the dock, 
and that a spillway is provided through the outer wall. The 
pumps are square wooden boxes extending through the floor 
of the pump well and to within a few inches of the bottom of 
the dock. 

Near the bottom of the pump barrel, which is 16 inches 
square, is the foot or suction valve, the detail construction of 
which is shown. About half way up the pump well there is 
a rocker arm, to each end of which is attached a pump rod and 
to one end of which the connecting rod is attached and delivers 
the motion from the line shaft above; the stroke of the pumps 
is 20 inches, and as they are single-acting they each deliver 
about 2 cubic feet of water per revolution. They operate at 
from 6o to 75 revolutions per minute. 

The pumping machinery on each side of the dock is operated 
by a vertical slide-valve engine having a cylinder 20 inches 
diameter by 24 inches stroke. There was no attempt in the 
power equipment to obtain high economy, as at the most 
they would operate but one or two hours a day. There are 
two upright boilers on each side having a diameter of 72 
inches and a height of 13 feet, built for a working pressure 
of 125 pounds. A pressure of from 80 to 90 pounds is found 
to be all that is required to operate the dock. 

The construction of floating docks and their development 
up to this time has been almost entirely in the hands of prac¬ 
tical men, and the details of their construction and equipment 
have been quite thoroughly worked out, but the hydraulic 


FLOATING DRYDOCKS. 


339 


principles involved and the structural strains involved in their 
use have received little attention and are not generally under¬ 
stood. 



WHiCo' S«C*TOO 
> of 6 cj** 
and Frunif, 



of Gat* r\ Ptace. 

FIG. 8. DETAILS OF FLOOD GATE. 



r* . 




Built by the 


FIG. J. TRANSVERSE SECTION OF ONE WING. 
SHOWING PUMPING ARRANGEMENT. 


U- - ?4‘ —* .H 












□□□□□□□ 

□□□□□□□ 




nnmnnnn 

* 



□unnnuu 

□□□□□□□ 

□□□□□□□ 

\ 





P\arv 


Tietjen & Lang Co, 
Hoboken, N. J. 

Faber du Faur & Donnelly, 
132 Nassau St., 

New York City, 
Engineers. 



Wrhcol Sectors 


FIG. 5. DETAILS OF FOOT VALVE 
AND PLUNGER. OF PUMP. 


FIG. 6. PILLOW BLOCK FOR LINE SHAFT AND COUNTER SHAFT. 


Fig. 16. —Machinery Details, io,ooo-Ton Floating Drydock. 


DISCUSSION. 

C. Ekstrand. —What material is used in bolting? 

The Author. —All drift bolts were of galvanized iron; on 
the extreme upper work, which is always above the water and 
can be frequently painted, black screw bolts were used. In 
the design of this dock, particularly the parts below the water, 
the study was to use as few screw bolts as possible. The only 










































































































































340 


FLOATING DRYDOCKS. 


long screw bolts are 134 inches diameter through the main 
trusses alongside of the longitudinal bulkheads; these were 
galvanized. When metal such as drift bolts is entirely in wood 
it will not deteriorate, but when used as through bolts it will 
rust in time, even when galvanized. 

F. W. Perry.— What is the use of the open bulkheads? 

The Author. —To give longitudinal strength and rigidity 
to the sections; they are made with openings so that the water 
may flow to the pumps. 

Mr. Post.—D o I understand that the dock will dock itself 
for repairs? 

The Author.— Yes. The method* is to detach the section 
to be repaired and turn it the narrow way; it will then go 
between the side walls and may be docked in the same man¬ 
ner as a vessel. This is one of the reasons for making the 
dock in sections. 

A. J. Proy t ost, Jr. —Has creosoted lumber been used? 

The Author.— No. We rely on dry lumber selected free 
from sap. 

R. S. Buck.— How were the keel blocks placed so as to con¬ 
form to the different .forms of keels? 

The Author.' —Nearly all iron vessels carry a docking 
plan and generally have a straight keel, but wooden vessels are 
sometimes very much out of shape. We have docked a side- 
wheel steamer used as a towboat on the Hudson River, the 
keel of which was 2?4 feet out of a straight line. This boat 
was built straight and had sagged to a double curve, the keel 
being down 23/2 feet in the center below the highest place, 
which was about two-thirds of the way from the center to the 
end. The ends dropped a foot below the highest point. In 
blocking for a vessel such as this we use patent keel blocks, 
that is, blocks composed of wedges that can be drawn in such 
a way as to be adjusted while the vessel is in place in the dock 
Every fourth block is usually made a patent or adjustable 
block, and when docking a vessel, the shape of which is in 
doubt, we arrange the blocking in a straight line, and then 
as soon as the vessel touches the blocks we haul on the patent 


FLOATING DRYDOCKS. 


341 


blocks. If the keel is straight, none of the blocks can be 
moved, as they will all be in touch with the bottom. If it is 
not straight, all will be hauled until they touch the keel. Then 
the vessel will be taken out of the dock and it will be pumped 
up, when the shape of the keel will be clearly shown by the 
patent blocks, and the intermediate blocks can all be built up 
to correspond, after which the vessel can be docked in the 
usual way. 

R. S. Buck.— What is the object of the arch form of truss? 

The Author.— The object is to get a good hold of the 
lower truss head; if you carry a straight member out to that 
point you will get very little actual connections coming in at 
such an acute angle, but by bringing the arch over we get a 
very good connection at that point, which takes the load 
off the wings when the dock is up, when there is nothing on 
but the ballast that is used to sink the dock. In the 10,000- 
ton dock we have to put in 500 tons of ballast to each section 
or 2,500 tons of ballast. When the dock is pumped up we have 
then a great bulk of stone piled in each wing and the dock is 
supported by a uniform pressure of water across the entire 
bottom. The center of that force will be at the center here; 
we have the weight of the structure and 500 tons on each 
side tending to break the dock in two in a reverse direction. 

P. H. Bevier.— Can you adjust the blocks without sending 
a diver down there? 

The Author.—W e don't use a diver, because it is very 
much cheaper to take the dock up. 

P. H. Bevier.— That don’t very often happen, does it? 

The Author. —No; there is a very general courtesy be¬ 
tween different docking companies as to explaining what a 
certain vessel is, and if they have blocked the vessel before, it 
is part of the dockmaster’s business to know the blocking. 

C. Ekstrand, —You haven’t mentioned anything about the 
greatest enemy to a sectional dock—floating* ice? 

The Author. —In my experience we never have had a 
dock blocked with ice—I can understand when you get in the 
southeast side of the harbor it may become quite a serious 


matter. 





342 


FLOATING DRYDOCKS 


C. Ekstrand. —I have seen occasionally where it took three 
clays to dock a tugboat, making five or six attempts each day. 

The Author. —We have never had any trouble in Hoboken. 
Of course, as ice accumulates it becomes quite a proposition 
to keep them clear. Sometimes we have had docks up so 
long that they have frozen over inside and it has been neces¬ 
sary to send men in with an axe and knock a hole in the ice 
so the water could run in. 

C. Ekstrand. —Are those gates made of cast iron, both 
gate and frame for it? 

The Author. —Yes. 

C. Ekstrand. —Wedge shape? 

The Author. —Yes. 

A. J. Provost, Jr. —Does the teredo destroy the dock? 

The Author. —No, the sheathing over felt seems to pro¬ 
tect them entirely; sheathed with rough boards, hemlock or 
spruce. 

A. J. Provost, Jr. —As a matter of fact, the teredo isn’t 
very bad in the harbor? 

The Author. —So bad that railways are eaten. 

A. J. Provost, Jr. —Don’t they get inside of the dock? 

The Author. —No, we have had no trouble with them. 

P. H. Bevier. —Do you have any trouble with swells on 
the surface of the water? 

The Author. —No, we have had no trouble. Of course, 
they are generally in protected places, reasonably protected. 

F. W. Perry. —In the sectional dock, when you get all the 
weight of the vessel on one section will she strain? 

The Author. —No, there is a play given in the locking 
logs, and when standing on the end of the dock the lines of 
the planks give you such an accurate line up of the dock that 
you can see the play of the locking logs ; you can then pump 
on any section by controlling the inlet; if a section gets high 
you will let the water in there. 

F. W. Perry. —You said you could approach very nearly 
the same condition the vessel is in while afloat. Does this de¬ 
pend entirely upon the judgment of the man operating the 









FLOATING DRYDOCKS. 


343 


dock? Is it possible to lift very much on one section or very 
little on another section and thereby strain the vessel ? 

The Author. —If he has a weak vessel on he puts battens 
on the vessel and lines them up. Now, if he pumps wrong, 
he will throw them out of line, and he simply pumps to keep 
them in line. 

C. Ekstrand.— As a matter of fact, every vessel changes 
its shape when it goes on drydock, more or less, especially 
the wooden vessels? 

The Author.— The most difficult vessels to dock are the 
Albany boats, the shallow boats. We have had every section 
in use in docking those vessels, and have had no trouble with 
them. 

C. Ekstrand.— When a vessel goes on drydock to have the 
machinery realigned, it is necessary to disconnect the shaft and 
make certain marks and make lines before docking and com¬ 
pare these with lines after docking, and you will find in ninety 
cases out of one hundred the two do not agree, and there is 
an appreciable difference. 

The Author. —We have no great difficulty in doing it. 

C. Ekstrand.— Isn’t it a fact that boats on the river- 

C. D. Pollock.— Are you building one of these docks at 
Norfolk or here? 

The Author. —In Norfolk. 

C. D. Pollock.— My impression is that on these river boats 
the sections are quite small ? 

The Author. —Yes, and, consequently, you haven’t got t^. 
pump them so nearly accurate as if they were larger. 

C. Ekstrand. —It depends upon the pump master? 

The Author. —In one case you have a man and pump that 
he knows what his pump is doing. At the same time he 
must have the best of machinery and know all that the ma¬ 
chinery can do. 

C. Ekstrand.— Isn’t it a fact that it takes more care and 
attention to operate a sectional dock than a balanced dock? 

The Author. —I don’t know. Of course, for the same size 
that would mean—we have no balanced dock that compares 













344 


FLOATING DRYDOCKS. 


in size to this large sectional dock. This large sectional dock 
will take five men on each side to handle the gates, two 
engineers and a dockmaster while it is operating. Of course, 
these men go back to other work when the vessel is docked. 

C. Ekstrand. —Isn’t it more of a strain on the dockmaster? 

The Author. —It doesn’t appeal so to me. Certainly, it is 
less care to operate a 2,000-ton dock than a io,ooo-ton dock. 

W. J. Baxter. —What is the depth of the blocks under¬ 
neath the bottom of the keel ? 

The Author. —In this case we have 3-foot blocks. 

W. J. Baxter. —You would want how much water under 
the bottom of the dock? 

The Author. —We have 30 feet and the dock draws 10 feet. 

W. J. Baxter. —Then, notwithstanding you have a 10,000- 
ton dock drawing 30 feet, you want 40 feet of water ? 

The Author. —Yes. 

W. J. Baxter. —Then for a basin dryclock you would have 
to spend much more money at first cost, but you could tal<u 
your io,ooo-ton ship in easier, if much damaged, if you had 
40 feet of water to dock her in? 

The Author. —But. certainly, if you have 40 feet of water 
in a basin dock it would cost a lot more. 

W. J. Baxter. —Isn’t that the reason in taking out vessels, 
whether merchant ships or war ships, and when docked under 
those circumstances and extensive repairs are necessary, that 
while in this dock they must be kept absolutely stationary and 
not subjected to the personal ecpiation, but absolutely free from 
personal equation, where things must be absolutely rigid, ab¬ 
solutely safe, isn’t the Government right in having basin drv- 
docks ? 

The Author. —As an engineer I support your view. The 
proper thing for the Government is to have basin drvdocks 
where they dock in that way. I understand the present plan 
is to have three longitudinal docking keels, and you can then 
put a vessel on a rigid foundation and have her entirelv satis¬ 
factory for any length of time. 

W. J. Baxter. —Suppose that it has to be done on a float¬ 
ing dock ? 






FLOATING DRYDOCKS. 


345 


1 he Author.— At the same time, while I would say that 
for the larger battleships I believe it is not well for the Gov- 
ei nment to take out all its smaller vessels in the larger docks, 
and that there should be floating docks for the large fleet of 
gunboats so that they can be docked more quickly and often and 
so kept up better. 

W. J. Baxter.— I think you will find a number of people 
who will agree with you in that respect. 

The Author.— And in the use of those docks they should 
g'et men who were trained. Judging from the number of ves¬ 
sels docked, the risk is very small, and is readily covered with 
maritime insurance, the loss is very small. 

W. J. Baxter.— I have been extremely interested in hear¬ 
ing this very able exposition, and I have learned more about 
floating docks than I have known before, but I think the other 
side has not had enough consideration, that is, the big-ship 
side. 

The impression has been gained here that the Government 
is against floating docks. That is not so. It is building one 
for the Philippines and using one at New Orleans. 

W. J. Baxter.— It is unfortunately, in this port, there is no 
very large commercial dock, but it is coming some day; on the 
other side are the docks where big* commercial work is being 
done. The floating docks are extremely necessary when well 
designed; we use the graving dock whenever we can and are 
delighted to use the floating dock when we cannot get the other. 

Mr. Holliday, being called upon, said: Civil Engineer Cox 
is here and in charge of a dock building at Sparrow Point, 
Maryland, and perhaps will want to say something. 

Mr. Cox.— I have very little to say. The subject has been 
well discussed. I am interested principally in the steel dock, 
because mine is a steel dock, and I never built a dock before. 
I was interested in what Mr. Donnelly had to say in regard to 
his opinion that the steel dock would never be a commercial 
success. I thought it would, but lack the experience, however. 
I was glad to learn that the pontoon dock started in ’6o or 
’70 was never completed ; however, I have found it on the Mis- 





346 


FLOATING DRYDOCKS. 


sissippi River, down below Algiers. I don’t know the history 
of that dock; don’t know what water it was in. Some people 
say it was sunk or lost. 

W ! . J. Baxter.— Wasn’t that made out of iron? 

Mr. Cox.—Yes. But that wasn’t brought up as evidence 
that steel would last forever. I want to know if it was in salt 
water. 

He was an advocate of the one-piece dock, his idea being that 
he could add on to the figures for first cost and start a sinking 
fund from that. 

I wanted to hear some discussion about the one-piece dock 
and would like to hear Mr. Donnelly’s ideas on the subject. 

Mr. Donnelly. —I have considered the one-piece dock, and 
it seems to me that if you undertake to make a structure 800 
or 1,000 feet long and endeavor to keep the depth of the bot¬ 
tom down to a reasonable figure, say, 20 feet, the proportion 
of length to depth -in the truss is such as to call for an enormous 
cross-section of metal, if you are to keep the deflection down to 
a reasonable figure. I am of the opinion that the problem can 
be satisfactorily solved in all its requirements by a sectional 
dock. 

Mr. Cox.—I mean a commercial dock. 

Mr. Donnelly. —Speaking of a commercial dock, you must 
come right down to the question whether it will pay or not; 
it isn’t a matter of the largest dock in New York Harbor. 
This dock has been a commercial success simply because it is 
built small enough. It will dock a vessel 525 feet long; that 
doesn’t go into the largest class, of which there are only a 
few vessels. As the vessel gets larger they have more compart¬ 
ments ; those vessels can hobble over to the other side, where 
thev have basin docks. Very few exceedinglv laro-e docks will 
do for the large vessels, and it is hardly reasonable 'for us to 
make them here if they have them on the other side. The 
question is, if you have your large docks here, will the vessel 
stav here? Not unless she absolutelv has to. 










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